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HX64098478 
QP40.B831902     Acompendofhumanp 


RECAP 


UIZCOMPENDS 


Physiology 


DR.  BRU  BAKER. 


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MORRIS'  ANATOMY. 

SECOND  EDITION. 

79 i  Illustrations,  of  which  2*4  are  Colored* 

Human  Anatomy.  A  Complete  Systematic  Treatise  by  Vari- 
ous Authors,  Including  Special  Sections  on  Surgical  and 
Topographical  Anatomy,  the  Skin,  and  Vestigial  and 
Abnormal  Structures.     Edited  by  Henry  Morris,  m.a.  and 


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From  The  Philadelphia  Medical  Journal. 

"  Of  all  the  text-books  of  moderate  size  on  human  anatomy  in  the  English 
language,  Morris'  is  undoubtedly  the  most  up-to-date  and  accurate.  .  .  . 
For  the  student,  the  surgeon,  or  for  the  general  practitioner  who 
desires  to  review  his  anatomy,  Morris'  is  decidedly  the  book  to  buy." 

A  Descriptive  Circular  of  Morris'  "Anatomy,"  with  Sample  Pages 
and  Colored  Illustrations,  will  be  sent  free  to  any  address. 


Tyson's  Practice  of  Medicine 

SECOND  EDITION, 
J  27  Illustrations,  Several  of    which  are  i)  Colors, 

The  Practice  of  Medicine.  A  Text-Book  for  Jhysicians  and 
Students,  with  Special  Reference  to  Diagnoss  and  Treat- 
ment. By  James  Tyson,  m.d.,  Professor  of  Medicine  in 
the  University  of  Pennsylvania';  Physician  lib  the  Uni- 
versity and  to  the  Philadelphia  Hospitals;  Ffllow  of  the 
College  of  Physicians  of  Philadelphia ;  Meriber  of  the 
Association  of  American  Physicians,  etc.  Second  F^ition. 
Octavo.     1222  pages.      127  Illustrations. 

Cloth,  net,  $5.50;   Sheep,  tif/,  £6.50 

jg^- This,  edition  has  been  entirely  reset  from  new  type. 
The  author  has  revised  it  carefully  and  thoroughly,  and  added 
much  new  material  and  37  new  illustrations. 

From  The  Therapeutic  Gazette. 

"  From  the  first  to  the  last  of  this  large  volume  of  nearly  1200  pages  we 
find  much  to  commend,  almost  nothing  to  criticise,  and  certainly  nothing  to 
contradict. 

"  It  is  in  the  writing  and  preparation  of  a  work  of  this  character  that  Dr. 
Tyson  stands  pre-eminent.  Those  of  the  profession — and  t>~rc  are  many  at 
this  time — who  have  been  fortunate  enough  to  have  been  his  pupils  during 
their  medical  student  days,  will  remember  that  he  brought  to  his  lectures  and 
to  his  writings  an  amount  of  industry  and  care  which  many  other  teachers 
failed  to  bring ;  and  those  who  know  him  best  as  an  author  and  teacher  have 
expected  that  his  book  on  the  Practice  of  Medicine,  when  it  appeared,  would 
be  a  credit  to  himself  and  would  increase  his  reputation  as  a  medical  author. 
This  belief  has  proved  correct.  .  .  .  We  look  forward  to  using  this  vol- 
ume upon  the  '  Practice  of  Medicine  '  more  than  any  of  the  others  which  grace 
our  library  shelves,  and  they  are  many  and  all  of  them  good." 

From  The  North  American  Practitioner,  Chicago. 

"  The  individuality  of  the  writer  is  clearly  manifest  in  the  clear  and 
practical  manner  in  which  diseases  are  described  and  their  treatment  expressed. 
.  .  .  The  succeeding  sections  upon  Diseases  of  the  Digestive,  Respiratory, 
Circulatory,  and  Nervous  Systems,  together  with  those  of  the  Blood,  Urinary 
Organs,  Constitutional  Diseases,  etc.,  are  so  full  as  to  well  serve,  in  each 
instance,  the  needs  of  the  specialist,  while  their  grouping  in  one  complete 
volume  renders  it  a  valuable  text-book  for  students,  and  the  one  above  any 
other  now  at  command  most  suited  to  the  present  needs  of  the  active  practi- 
tioner. It  is  the  best  representative  of  the  practical  application  of 
modern  research  and  discovery  to  the  treatment  of  diseases  now  at 
the  command  of  the  medical  profession." 


SYBASE'  ON  RECENT  MEDICAL  LITERATURE. 

QOUid'S  The  Standard 

M/t        *•  «  Medical 

iVlCCflCfl.]  Reference  Books. 


Dictionaries. 


130,000  HAVE 
BEEN  SOLD. 


BY  GEORGE  M.  GOULD,  A.M.,  M.D., 

Editor  of  American  Medicine. 


THE  ILLUSTRATED  DICTIONARY  OF  MEDICINE,  BI- 
OLOGY, AND  ALLIED  SCIENCES,  including  the  pro- 
nunciation, ACCENTUATION,  DERIVATION,  AND  DEFINITION  OF  THE 
TERMS  USED  IN  MEDICINE  AND  THOSE  SCIENCES  COLLATERAL  TO  IT: 
BIOj.OGY  (ZOOLOGY  AND  BOTANY),  CHEMISTRY,  DENTISTRY,  PHARMA- 
COLOGY, microscopy,  etc.  With  many  Useful  Tables  and  numerous 
Fine  Illustrations.  Large  Square  Octavo.  1 633  pages.  Fifth  Edition 
row  ready.  Full  Sheep,"  or  Half  Dark-Green  Leather,  net,  $10.00  ; 

With  Thumb  Index,  net,  $11.00;  Half  Russia,  Thumb  Index,  net,  $12.00 

THE    STUDENT'S    MEDICAL    DICTIONARY,     including  all 

THE  WORDS  AND  PHRASES  GENERALLY  USED  IN  MEDICINE,  WITH 
THEIR    PROPER   PRONUNCIATION   AND    DEFINITIONS,    BASED   ON    RECENT 

MEDICAL  literature.  With  Tables  of  the  Bacilli,  Micrococci,  Leuko- 
mains,  Ptomains,  etc.,  of  the  Arteries,  Muscles,  Nerves,  Ganglia,  and 
Plexuses ;  Mineral  Springs  of  the  U.  S.,  etc.  Eleventh  Edition, 
Illustrated.  Revised,  Enlarged  by  over  150  pages.  Small  Square 
Octavo.    Half  Dark  Leather,  net,  $2.50;  with  Thumb  Index,  net,  $3.00 

(       THE  POCKET  PRONOUNCING  MEDICAL  LEXICON.   30,000 
words    pronounced  and    denned.      Containing  all    the  Words,  their 
Definition  and  Pronunciation  that  the  Student  generally  comes  in  contact 
<4  with  ;  also  elaborate  Tables  of  the  Arteries,   Muscles,   Nerves,   Bacilli, 

etc.,  etc.;  a  Dose  List  in  both  English  and  Metric  Systems,  etc.,  arranged 
in  a  most  convenient  form  for  reference  and  memorizing.  Fourth  Edition, 
837  pages.     64U10. 

Full  Limp  Leather,  Gilt  Edges,  net,  $1.00;  Thumb  Index,  net,  $1.25 

THE  POCKET  CYCLOPEDIA  OF  MEDICINE  AND  SUR- 
GERY. Edited  by  Drs.  George  M.  Gould  and  W.  L.  Pyle.  A 
Concise  Practical  Handbook  containing  a  vast  amount  of  Information  Sys- 
tematically Arranged  so  as  to  be  of  the  Greatest  Service  to  the  Student. 
Uniform  with  "Gould's  Pocket  Dictionary."     64mo. 

Full  Limp  Leather,  Round  Corners,  Gilt  Edges,  net,  $1.00 

Thumb  Index,  net,  $1.25 


Full  descriptive  circulars  and  sample  pages  sent  free  upon  application. 


HUMAN  PHYSIOLOGY 


ELEVENTH   EDITION 


BRUBAKER 


From  The  Southern  Clinic. 

"  We  know  of  no  series  of  books  issued  by  any  house  that  so  fully  meets  our 
approval  as  these  ?Quiz-Compends?.  They  are  well  arranged,  full,  and  con- 
cise, and  are  really  the  best  line  of  text-books  that  could  be  found  for  either 
student  or  practitioner."  

BLAKISTON'S  ?QUIZ=COMPENDS? 

The  Best  Series  of  Manuals  for  the  Use  of  Students. 

Price  of  each,  Cloth,  $0.80  net.     Interleaved,  for  taking  Notes,  $1.00  net. 

4®=-These  Compends  are  based  on  the  most  popular  text-books  and  the  lectures  of 
prominent  professors,  and  are  kept  constantly  revised,  so  that  they  may  thoroughly  repre- 
sent the  present  state  of  the  subjects  upon  which  they  treat. 

*3-The  authors  have  had  large  experience  as  Quiz-Masters  and  attacnes  of  colleges, 
and  are  well  acquainted  with  the  wants  of  students.  '_  . 

*5-They  are  arranged  in  the  most  approved  form,  thorough  and  concise,  containing 
over  600  fine  illustrations,  inserted  wherever  they  could  be  used  to  advantage. 

4^»Can  be  used  by  students  of  any  college. 

Ji&>  They  contain   information  nowhere  else  collected  in  such  a  condensed,  practical 

shape. 

Illustrated  Circular  Free.   *<-     * 

No  1  POTTER'S  ANATOMY.  Sixth  Revised  and  Enlarged  Edition.  Including 
Visceral  Anatomy.  Can  be  used  with  either  Morris' or  Gray's  Anatomy.  _ii7  Illus- 
trations and  16  Lithographic  Plates  of  Nerves  and  Arteries,  with  Explanatory  Tables,  etc. 

No.  2.  HUGHES.  PRACTICE  OF  MEDICINE.  Parti.  Sixth  Edition,  Revised, 
Enlarged,  and  Improved. 

No  3  HUGHES.  PRACTICE  OF  MEDICINE.  Part  II.  Sixth  Edition,  Revised, 
Enlarged,  and  Improved.  These  two  books  furnish  a  complete  set  of  notes  on  the 
Practice  of  Medicine,  including  Nervous  and  Mental  Diseases. 

No.  4.  BRUBAKER.  PHYSIOLOGY.  nth  Edition,  with  new  Illustrations  and 
a  Table  of  Physiological  Constants.    Enlarged  and  Revised. 

Xo  «;  LANDIS.  OBSTETRICS.  Sixth  Edition.  Revised  and  Edited  by  Wm.  H 
Wells,  m.d.,  Instructor  Jefferson  Medical  College,  Philadelphia.     47  Illustrations. 

No.  6.  POTTER.  MATERIA  MEDICA,  THERAPEUTICS,  AND  PRESCRIP- 
TION WRITING.    Sixth  Revised  Edition. 

No  7       WELLS.    GYNAECOLOGY.    Second  Edition.    With  many  Illustrations. 

No.  8*.  GOULD  and  PYLE.  DISEASES  OF  THE  EYE  AND  REFRACTION. 
Including  Treatment  and  Operations  and  a  Section  on  Local  Therapeutics.  With 
Formula:  and  109  Illustrations,  several  of  which  are  in  Colors.    Second  Edition. 

No  Q  HORWITZ'S  SURGERY,  Minor  Surgery,  and  Bandaging.  Fifth  Edition, 
Enlarged  and  Improved.    With  98  Formulae  and  167  Illustrations. 

No.  10.  LEFFMANN.  CHEMISTRY.  Inorganic  and  Organic.  Fourth  Edition. 
Including  Urinalysis,  Animal  Chemistry,  Chemistry  of  Milk,  Blood,  1  issues,  the  Se- 
cretions, etc.  t 

No.  11.  STEWART.  PHARMACY.  Fifth  Edition.  Based  upon  Prof.  Remington  s 
Text-Book  of  Pharmacy. 

No.  12.  BALLOU.  VETERINARY  ANATOMY  AND  PHYSIOLOGY.  With 
29  graphic  Illustrations. 

No  13  WARREN.  DENTAL  PATHOLOGY  AND  DENTAL  MEDICINE. 
'Third  Edition,  Illustrated.  Containing  all  the  most  noteworthy  points  of  interest  to 
the  Dental  Student,  and  a  Section  on  Emergencies. 

No.  14.  HATFIELD.  DISEASES  OF  CHILDREN.  Colored  Plate.  Third  Edi- 
tion, Revised  and  Enlarged. 

No    15.     THAYER.     GENERAL  PATHOLOGY.    With  78  Illustrations. 

No.  16.    SCHAMBERG.      DISEASES  OF  THE  SKIN.      Second   Edition.     Illus. 

No*.  17.     CUSHING.     HISTOLOGY.     With  many  Illustrations. 

No.  18.     THAYER.     SPECIAL  PATHOLOGY.     With  34  Illustrations. 

Price,  each,  $0.80  net.    Interleaved,  for  taking  Notes,  $1.00  net. 

P.  BLAKISTON'S  SON  &  CO.,  PUBLISHERS, 

PHILADELPHIA. 


?QUIZ-COIVlF>ENDS?     NO.  4. 

A  COMPEND 

OF 

HUMAN  PHYSIOLOGY 

ESPECIALLY  ADAPTED   FOR  THE   USE  OF 
MEDICAL  STUDENTS 

BY 

ALBERT    P.  BRUBAKER,  A.M.,  M.D. 

ADJUNCT    PROFESSOR    OF    PHYSIOLOGY  AND  HYGIENE  IN  THE    JEFFERSON  MEDICAL  COL- 
LEGE ;    PROFESSOR  OF  PHYSIOLOGY  IN  THE  PENNSYLVANIA  COLLEGE    OF    DENTAL 
SURGERY;    LECTURER   ON   ANATOMY   AND   PHYSIOLOGY   IN   THE    DREXEL  ' 
INSTITUTE     OF   ART,    SCIENCE,    AND    INDUSTRY  ;      FELLOW    OF 
THE   COLLEGE   OF   PHYSICIANS   OF    PHILADELPHIA. 

ELEVENTH   EDITION,   REVISED   AND   ENLARGED 
WITH   ILLUSTRATIONS 

AND 

A  TABLE  OF  PHYSIOLOGIC  CONSTANTS 


PHILADELPHIA 

P.  BLAKISTON'S  SON   &   CO. 

1012   WALNUT  STREET 
1902 


Entered  according  to  Act  of  Congress,  in  the  year  1902,  by 

P.  BLAKISTON'S  SON   &  CO. 

In  the  Office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


T>£3 


PREFACE  TO  THE  ELEVENTH  EDITION. 


A  new  edition  of  the  Corapend  of  Physiology  having  been  called  for  the 
opportunity  has  again  been  taken  to  revise  some  of  the  old,  and  to  insert 
some  new  paragraphs  to  various  parts  of  the  text,  changes  which  it  is 
believed  will  be  of  value  to  the  student  during  his  attendance  on  the 
lectures.  It  is  hoped  the  Compend  will  continue  to  meet  the  needs  of 
the  medical  student. 

Albert  P.  Brubaker. 

September  I,  1902. 


TABLE  OF  CONTENTS. 


PAGE, 

Introduction, 9 

General  Structure  of  the  Animal  Body, u 

Chemic  Composition  of  the  Human  Body, 15 

Physiology  of  the  Cell, S3 

Histology  Of  the  Epithelial  and  Connective  Tissues,    ....    39 

Mechanism  of  the  Skeleton, 46 

General  Physiology  of  Muscular  Tissue, 50 

Special  Physiology  of  Muscles, 63 

Physiology  of  Nerve  Tissue, 69 

Foods  and  Dietetics, 86 

Digestion, 95 

Absorption, in 

Blood, 119 

Circulation  of  the  Blood, -. 125 

Respiration, ' 135 

Animal  Heat, 143 

Secretion, 145 

Mammary  Glands, 148 

Vascular  Glands,      150 

Excretion, 155 

Kidneys,   ....  155 

Liver, 163 

Skin, 168 

Cerebro-Spinal  Axis, 171 

Spinal  Cord,      172 

Spinal  Nerves, .174 

vii 


vill  TABLE   OF    CONTENTS. 

PAGE. 

Cranial  Nerves, 183 

Medulla  Oblongata, 197 

Pons  Varolii, 201 

Crura  Cerebri, 202 

Corpora  Quadrigemina, 203 

Corpora  Striata  and  Optic  Thalami, 204 

Cerebellum, .   .       ......  205 

Cerebrum, 207 

Cerebral  Localization  of  Function, 214 

Sympathetic  Nervous  System, 218 

Sense  of  Touch, 222 

.Sense  of  Taste, 223 

Sense  of  Smell, 225 

Sense  of  Sight,         226 

Sense  of  Hearing,    .   .   . 237 

Voice  and  Speech, 245 

Embryology,     248 

Generative  Organs  of  the  Female, 248 

Generative  Organs  of  the  Male, 251 

Development  of  Accessory  Structures, 252 

Development  of  the  Embryo, 257 

Table  of  Physiologic  Constants, 263 

Table  Showing  Relation  of  Weights  and  Measures, 266 

Index,      ....  267 


A  COMPEND 


OF 


HUMAN  PHYSIOLOGY. 


Introduction. — An  animal  organism  in  the  living  condition  exhibits  a 
series  of  phenomena  which  relate  to  growth,  movement,  mentality,  and 
reproduction.  During  the  period  preceding  birth,  as  well  as  during  the 
period  included  between  birth  and  adult  life,  the  individual  grows  in  size 
and  complexity  from  the  introduction  and  assimilation  of  material  from 
without.  Throughout  its  life  the  animal  exhibits  a  series  of  movements, 
in  virtue  of  which  it  not  only  changes  the  relation  of  one  part  of  its  body 
to  another,  but  also  changes  its  position  in  space.  If,  in  the  execution  of 
these  movements,  the  parts  are  directed  to  the  overcoming  of  opposing 
forces,  such  as  gravity,  friction,  cohesion,  elasticity,  etc.,  the  animal  may 
be  said  to  be  doing  work.  The  result  of  normal  growth  is  the  attainment 
of  a  physical  development  that  will  enable  the  animal,  and,  more  espe- 
cially, man,  to  perform  the  work  necessitated  by  the  nature  of  its  environ- 
ment and  the  character  of  its  organization.  In  man,  and  probably  in  lower 
animals  as  well,  mentality  manifests  itself  as  intellect,  feeling,  and  volition. 
At  a  definite  period  in  the  life  of  the  animal  it  reproduces  itself,  in  conse- 
quence of  which  the  species  to  which  it  belongs  is  perpetuated. 

The  study  of  the  phenomena  of  growth,  movement,  mentality,  and  re- 
production constitutes  the  science  of  Animal  Physiology.  But  as  these 
general  activities  are  the  resultant  of  and  dependent  on  the  special  activities 
of  the  individual  structures  of  which  an  animal  body  is  composed,  Physi- 
ology in  its  more  restricted  and  generally  accepted  sense  is  the  science 
which  investigates  the  actions  or  functions  of  the  individual  organs  and 
tissues  of  the  body  and  the  physical  and  chemic  conditions  which  underlie 
and  determine  them, 


10  HUMAN   PHYSIOLOGY. 

This  may  naturally  be  divided  into  : 

1.  Special  physiology,  the  object  of  which  is  a  study  of  the  vital  phe- 
nomena or  functions  exhibited  by  the  organs  of  any  individual  animal. 

2.  Comparative  physiology,  the  object  of  which  is  a  comparison  of  the 
vital  phenomena  or  functions  exhibited  by  the  organs  of  two  or  more 
animals,  with  a  view  to  unfolding  their  points  of  resemblance  or  dissimi- 
larity. 

Human  physiology  is  that  department  of  physiologic  science  which 
has  for  its  object  the  study  of  the  functions  of  the  organs  of  the  human 
body  in  a  state  of  health. 

Inasmuch  as  the  study  of  function,  or  physiology,  is  associated  with  and 
dependent  on  a  knowledge  of  structure,  or  anatomy,  it  is  essential  that  the 
student  should  have  a  general  acquaintance  not  only  with  the  structure  of 
man,  but  with  that  of  typical  forms  of  lower  animal  life  as  well. 

If  the  body  of  any  animal  be  dissected,  it  will  be  found  to  be  composed 
of  a  number  of  well-defined  structures,  such  as  heart,  lungs,  stomach, 
brain,  eye,  etc.,  to  which  the  term  organ  was  originally  applied,  for  the 
reason  that  they  were  supposed  to  be  instruments  capable  of  performing 
some  important  act  or  function  in  the  general  activities  of  the  body. 
Though  the  term  organ  is  usually  employed  to  designate  the  larger  and 
more  familiar  structures  just  mentioned,  it  is  equally  applicable  to  a  large 
number  of  other  structures  which,  though  possibly  less  obvious,  are  equally 
important  in  maintaining  the  life  of  the  individual — e.  g.,  bones,  muscles, 
nerves,  skin,  teeth,  glands,  blood-vessels,  etc.  Indeed,  any  complexly  or- 
ganized structure  capable  of  performing  some  function  may  be  described  as 
an  organ.  A  description  of  the  various  organs  which  make  up  the  body 
of  an  animal,  their  external  form,  their  internal  arrangement,  their  rela- 
tions to  one  another,  constitutes  the  science  of  Animal  Anatomy. 

This  may  naturally  be  divided  into  : 

1.  Special  anatomy,  the  object  of  which  is  the  investigation  of  the  con- 
struction   form,  and  arrangement  of  the  organs  of  any  individual  animal. 

2.  Comparative  anatomy,  the  object  of  which  is  a  comparison  of  the 
organs  of  two  or  more  animals,  with  a  view  to  determining  their  points 
of  resemblance  or  dissimilarity. 

If  the  organs,  however,  are  subjected  to  a  further  analysis,  they  can  be 
resolved  into  simple  structures,  apparently  homogeneous,  to  which  the 
name  tissue  has  been  given  —  e.  g.,  epithelial,  connective,  muscle,  and 
nerve  tissue.  When  the  tissues  are  subjected  to  a  microscopic  analysis,  it 
is  found  that  they  are  not  homogeneous  in  structure,  but  composed  of  still 


GENERAL   STRUCTURE   OF   THE   ANIMAL    BODY.  11 

simpler  elements,  termed  cells  and  fibers.  The  investigation  of  the  in- 
ternal structure  of  the  organs,  the  physical  properties  and  structure  of  the 
tissues,  as  well  as*  the  structure  of  their  component  elements,  the  cells 
and  fibers,  constitutes  a  department  of  anatomic  science  known  as  His- 
tology, or  as  it  is  prosecuted  largely  with  the  microscope,  Microscopic 
Anatomy. 

Human  anatomy  is  that  department  of  anatomic  science  which  has 
for  its  object  the  investigation  of  the  construction  of  the  human  body. 

GENERAL    STRUCTURE    OF    THE   ANIMAL    BODY. 

The  body  of  every  animal,  from  fish  to  man,  may  be  divided  into  — 

1.  An  axial  and 

2.  An  appendicular  portion.  The  axial  portion  consists  of  the  bead,  neck, 
and  trunk  ;  the  appendicular  portion  consists  of  the  anterior  and  pos- 
terior limbs  or  extremities. 

The  axial  portion  of  all  mammals,  to  which  class  man  zoologically  be- 
longs, as  well  as  of  all  birds,  reptiles,  amphibians,  and  fish,  is  character- 
ized by  the  presence  of  a  bony,  segmented  axis,  which  extends  in  a  longi- 
tudinal direction  from  before  backward,  and  which  is  known  as  the  vertebral 
column  or  backbone.  In  virtue  of  the  existence  of  this  column  all  the 
classes  of  animals  just  mentioned  form  one  great  division  of  the  animal 
kingdom,  the  Vertebrata. 

Each  segment,  or  vertebra,  of  this  axis  consists  of — 

1.  A  solid  portion,  known  as  the  body  or  centrum,  and 

2.  A  bony  arch  arising  from  the  dorsal  aspect  and  surmounted  by  a  spine- 
like process. 

At  the  anterior  extremity  of  the  body  of  the  animal  the  vertebne  are 
variously  modified  and  expanded,  and,  with  the  addition  of  new  elements, 
form  the  skull  ;  at  the  posterior  extremity  they  rapidly  diminish  in  size,  and 
terminate  in  man  in  a  short,  tail-like  process.  In  many  animals,  however, 
the  vertebral  column  extends  for  a  considerable  distance  beyond  the  trunk 
into  the  tail.  The  vertebral  column  may  be  regarded  as  the  foundation 
element  in  the  plan  of  organization  of  all  the  higher  animals  and  the  center 
around  which  the  rest  of  the  body  is  developed  and  arranged  with  a  certain 
degree  of  conformity.  In  all  vertebrate  animals  the  bodies  of  the  segments 
of  the  vertebral  column  form  a  partition  which  serves  to  divide  the  trunk  of 
the  body  into  two  cavities  —  viz.,  the  dorsal  and  the  ventral. 


12 


HUMAN    PHYSIOLOGY. 


Fig. 


—Diagrammatic  Longitudinal 
Section  of  the  Body< 


V,  V.  Bodies  of  the  vertebrae  which  divide  the 
body  into  the  dorsal  and  ventral  cavities. 
a,  a' .  The  dorsal  cavity.  C,/'.  The  ab- 
"*  dominal  and  thoracic  divisions  of  the  ven- 
tral cavity,  separated  from  each  other  by 
a  transverse  muscular  partition,  the  dia- 
phragm d.  B.  The  brain.  Sp.  C.  The 
spinal  cord.  e.  The  esophagus.  S.  The 
stomach,  from  which  continues  the  intes- 
tine to  the  opening  at  the  posterior  portion 
of  the  body.  /.  The  liver.  /.  The  pan- 
creas, k.  The  kidney,  o.  The  bladder. 
/'.  The  lungs,    h.  The  heart. 


The  dorsal  cavity  is  found 
not  only  in  the  trunk,  but  also  in 
the  head.  It  walls  are  formed 
partly  by  the  arches  which  arise 
from  the  posterior  or  dorsal  sur- 
face of  the  vertebrae  and  partly 
by  the  bones  of  the  skull.  If  a 
longitudinal  section  be  made 
through  the  center  of  the  verte- 
bral column,  and  including  the 
head,  the  dorsal  cavity  will  be 
observed  running  through  its 
entire  extent.  (See  Fig.  i.) 
Though  for  the  most  part  it  is 
quite  narrow,  at  the  anterior  ex- 
tremity it  is  enlarged  and  forms 
the  cavity  of  the  skull.  This 
cavity  is  lined  by  a  membranous 
canal,  the  neural  canal,  in  which 
is  contained  the  brain  and  the 
neural  or  spinal  cord.  Through 
openings  in  the  sides  of  the  dor- 
sal cavity  nerves  pass  out  which 
connect  the  brain  and  spinal  cord 
with  all  the  structures  of  the 
body. 

The  ventral  cavity  is  con- 
fined mainly  to  the  trunk  of  the 
body.  Its  walls  are  formed  by 
muscles  and  skin,  strengthened 
in  most  animals  by  bony  arches, 
the  ribs.  Within  the  ventral 
cavity  is  contained  a  rnus- 
culo-membranous  tube  or  canal 
known  as  the  alimentary  or 
food  canal,  which  begins  at  the 
mouth  on  the  ventral  side  of  the 
head,  and,  after  passing  through 
the  neck  and  trunk,  terminates 
at  the  posterior  extremity  of  the 


GENERAL  STRUCTURE  OF  THE  ANIMAL  BODY.  13 

trunk  at  the  anus.     It  may  be  divided  into  mouth,  pharynx,  esophagus, 
stomach,  small  and  large  intestines. 

In  all  mammals  the  ventral  cavity  is  divided  by  a  musculo-membranous 
partition  into  two  smaller  cavities,  the  thorax  and  abdomen.  The  former 
contains  the  lungs,  heart  and  its  great  blood-vessels,  and  the  anterior  part 
of  the  alimentary  canal,  the  gullet  or  esophagus  ;  the  latter  contains  the 
continuation  of  the  alimentary  canal — that  is,  the  stomach  and  intestines — 
and  the  glands  in  connection  with  it,  the  liver  and  pancreas.  In  the  pos- 
terior portion  of  the  abdominal  cavity  are  found  the  kidneys,  ureters,  and 
bladder,  and  in  the  female  the  organs  of  reproduction.  The  thoracic  and 
abdominal  cavities  are  each  lined  by  a  thin  serous  membrane,  known,  re- 
spectively, as  the  pleural  and  peritoneal  membranes,  which,  in  addition,  are 
reflected  over  the  surfaces  of  the  organs  contained  within  them.  The  ali- 
mentary canal  and  the  various  cavities  connected  with  it  are  lined  throughout 
by  a  mucous  membrane.  The  surface  of  the  body  is  covered  by  the  skin. 
This  is  composed  of  an  inner  portion,  the  derma,  and  an  outer  portion,  the 
epidermis.  The  former  consists  of  fibers,  blood-vessels,  nerves,  etc.;  the 
latter  of  layers  of  scales  or  cells.  Embedded  within  the  skin  are  numbers  of 
glands,  which  exude,  in  the  different  classes  of  animals,  sweat,  oily  matter, 
etc.  Projecting  from  the  surface  of  the  skin  are  hairs,  bristles,  feathers, 
claws.    Beneath  the  skin  are  found  muscles,  bones,  blood-vessels,  nerves,  etc. 

The  appendicular  portion  of  the  body  consists  of  two  pairs  of  sym- 
metric limbs,  which  project  from  the  sides  of  the  trunk,  and  which  bear  a 
determinate  relation  to  the  vertebral  column.  They  consist  fundamentally 
of  bones,  surrounded  by  muscles,  blood-vessels,  nerves  and  lymphatics. 
The  limbs,  though  having  a  common  plan  of  organization,  are  modified  in 
form  and  adapted  for  prehension  and  locomotion  in  accordance  with  the 
needs  of  the  animal. 

Anatomic  Systems. — All  the  organs  of  the  body  which  have  certain 
peculiarities  of  structure  in  common  are  classified  by  anatomists  into  systems 
— e.  g.,  the  bones,  collectively,  constitute  the  bony  or  osseous  system  ;  the 
muscles,  the  nerves,  the  skin,  constitute,  respectively,  the  muscular,  the 
nervous,  and  the  tegumentary  systems. 

Physiologic  Apparatus. — More  important  from  a  physiologic  point 
of  view  than  a  classification  of  organs  based  on  similarities  of  structure 
is  the  natural  association  of  two  or  more  organs  acting  together  for  the 
accomplishment  of  some  definite  object,  and  to  which  the  term  physiologic 
apparatus  has  been  applied.     While  in  the  community  of  organs  which 


f 


14  HUMAN    PHYSIOLOGY. 

together  constitute  the  animal  body  each  one  performs  some  definite  func- 
tion, and  the  harmonious  cooperation  of  all  is  necessary  to  the  life  of  the 
individual,  everywhere  it  is  found  that  two  or  more  organs,  though  per- 
forming totally  distinct  functions,  are  cooperating  for  the  accomplishment 
of  some  larger  or  compound  function  in  which  their  individual  functions 
are  blended — e.  g.,  the  mouth,  stomach,  and  intestines,  with  the  glands 
connected  with  them,  constitute  the  digestive  apparatus,  the  object  or  func- 
tion of  which  is  the  complete  digestion  of  the  food.  The  capillary  blood- 
vessels and  lymphatic  vessels  of  the  body,  and  especially  those  in  relation 
to  the  villi  of  the  small  intestine,  constitute  the  absorptive  apparatus,  the 
function  of  which  is  the  introduction  of  new  material  into  the  blood.  The 
heart  and  blood-vessels  constitute  the  circulatory  apparatus,  the  function 
of  which  is  the  distribution  of  blood  to  all  portions  of  the  body.  The 
lungs  and  trachea,  together  with  the  diaphragm  and  the  walls  of  the  chest, 
constitute  the  respiratory  apparatus,  the  function  of  which  is  the  introduc- 
tion of  oxygen  into  the  blood  and  the  elimination  from  it  of  carbon  dioxid 
and  other  injurious  products.  The  kidneys,  the  ureters,  and  the  bladder  con- 
stitute the  urinary  apparatus.  The  skin,  with  its  sweat-glands,  constitutes 
the  perspiratory  apparatus,  the  functions  of  both  being  the  excretion  of 
waste  products  from  the  body.  The  liver,  the  pancreas,  the  mammary 
glands,  as  well  as  other  glands,  each  form  a  secretory  apparatus  which 
elaborates  some  specific  material  necessary  to  the  nutrition  of  the  indi- 
.  vidual.  The  functions  of  these  different  physiologic  apparatus — e.  g., 
digestion,  absorption  of  food,  elaboration  of  blood,  circulation  of  blood, 
respiration,  production  of  heat,  secretion,  and  excretion — are  classified  as 
nutritive  functions,  and  have  for  their  final  object  the  preservation  of  the 
individual. 

The  nerves  and  muscles  constitute  the  nervo-muscular  apparatus,  the 
function  of  which  is  the  production  of  motion.  The  eye,  the  ear,  the  nose, 
the  tongue,  and  the  skin,  with  their  related  structures,  constitute,  respectively, 
the  visual,  auditory,  olfactory,  gustatory,  and  tactile  apparatus,  the  func- 
tion of  which,  as  a  whole,  is  the  reception  of  impressions  and  the  trans- 
mission of  nerve  impulses  to  the  brain,  where  they  give  rise  to  visual, 
auditory,  olfactory,  gustatory,  and  tactile  sensations. 

The  brain,  in  association  with  the  sense  organs,  forms  an  apparatus 
related  to  mental  processes.  The  larynx  and  its  accessory  organs — the 
lungs,  trachea,  respiratory  muscles,  the  mouth  and  resonant  cavities  of  the 
face — form  the  vocal  and  articulating  apparatus,  by  means  of  which  voice 
and  articulate  speech  are  produced.  The  functions  exhibited  by  the 
apparatus  just  mentioned — viz.,  motion,  sensation,  language,  mental  and 


CHEMIC   COMPOSITION   OF   THE    HUMAN    BODY.  15 

moral  manifestations — are  classified  as  Junctions  of  relation,  as  they  serve 
to  bring  the  individual  into  conscious  relationship  with  the  external  world. 

The  ovaries  and  the  testes  are  the  essential  reproductive  organs,  the  for- 
mer producing  the  germ-cell,  the  latter  the  spermatic  element;  together 
with  their  related  structures, — the  fallopian  tubes,  uterus,  and  vagina  in  the 
female,  and  the  urogenital  canal  in  the  male, — they  constitute  the  reproduc- 
tive apparatus  characteristic  of  the  two  sexes.  Their  cooperation  results  in 
the  union  of  the  germ-cell  and  spermatic  element  and  the  consequent  de- 
velopment of  a  new  being.  The  function  of  reproduction  serves  to  per- 
petuate the  species  to  which  the  individual  belongs. 

The  animal  body  is  therefore  not  a  homogeneous  organism,  but  one  com- 
posed of  a  large  number  of  widely  dissimilar  but  related  organs.  But  as 
all  vertebrate  animals  have  the  same  general  plan  of  organization,  there  is 
a  marked  similarity  both  in  form  and  structure  among  corresponding  parts 
of  different  animals.  Hence  it  is  that  in  the  study  of  human  anatomy  a 
knowledge  of  the  form,  construction,  and  arrangement  of  the  organs  in 
different  types  of  animal  life  is  essential  to  its  correct  interpretation  ;  also 
it  is  that  in  the  investigation  and  comprehension  of  the  complex  problems 
of  human  physiology  a  knowledge  of  the  functions  of  the  organs  as  they 
manifest  themselves  in  the  different  types  of  animal  life  is  indispensable. 
As  many  of  the  functions  of  the  human  body  are  not  only  complex,  but 
the  organs  exhibiting  them  are  practically  inaccessible  to  investigation,  we 
must  supplement  our  knowledge  and  judge  of  their  functions  by  analogy, 
by  attributing  to  them,  within  certain  limits,  the  functions  revealed  by  ex- 
perimentation upon  the  corresponding  but  simpler  organs  of  lower  animals. 
This  experimental  knowledge,  corrected  by  a  study  of  the  clinical  phe- 
nomena of  disease  and  the  results  of  post-mortem  investigations,  forms  the 
basis  of  modern  human  physiology. 


CHEMIC  COMPOSITION   OF  THE  HUMAN 

BODY. 

Since  it  has  been  demonstrated  that  everv_exhihition_of  functional  activ- 
ity is  associated  with  changes  of  structure,  it  has  been  apparent  that  a 
knowledge  of  the^chemic  composition  of  the  body,  not  only  when  in  a  state 
of  rest,  but  to  a  far  greater  degree  when  in  a  state  of  activity,  is  necessary 
to  a  correct  understanding  of  the  intimate  nature  of  physiologic  processes. 
Though  the  analysis  of  the  dead  body  is  comparatively  easy,  the  determina- 


16  HUMAN    PHYSIOLOGY. 

tion  of  the  successive  changes  in  composition  of  the  living  body  is  attended 
with  many  difficulties.  The  living  material,  the  bioplasm,  is  not  only 
complex  and  unstable  in  composition,  but  extremely  sensitive  to  all  physical 
and  chemic  influences.  The  methods,  therefore,  which  are  employed  for 
analysis  destroy  its  composition  and  vitality,  and  the  products  which  are 
obtained  are  peculiar  to  dead  rather  than  to  living  material. 
Chemic  analysis,  therefore,  may  be  directed — 

1.  To  the  determination  of  the  composition  of  the  dead  body. 

2.  To  the  determination  of  the  successive  changes  in  composition  which 
the  living  bioplasm  undergoes  during  functional  activity. 

A  chemic  analysis  of  the  dead  body,  with  a  view  to  disclosing  the  sub- 
stances of  which  it  is  composed,  their  properties,  their  intimate  structure, 
their  relationship  to  one  another,  constitutes  what  might  be  termed  Chemic 
Anatomy.  An  investigation  of  the  living  material  and  of  the  successive 
changes  it  undergoes  in  the  performance  of  its  functions  constitutes  what 
has  been  termed  Chemic  Physiology  or  Physiologic  Chemistry. 

By  chemic  analysis  the  animal  body  can  be  reduced  to  a  number  of  liquid 
and  solid  compounds  which  belong  to  both  the  inorganic  and  organic 
worlds.  These  compounds,  resulting  from  a  proximate  analysis,  have  been 
termed  proximate  principles.  That  they  may  merit  this  term,  however, 
they  must  be  obtained  in  the  form  under  which  they  exist  in  the  living 
condition.  The  organic  compounds  consist  of  representatives  of  the  carbo- 
hydrate, fatty,  and  proteid  groups  of  organic  bodies  ;  the  inorganic  com- 
pounds consist  of  water,  various  acids,  and  inorganic  salts. 

The  compounds  or  proximate  principles  thus  obtained  can  be  further 
resolved  by  an  ultimate  analysis  into  a  small  number  of  chemic  elements 
which  are  identical  with  elements  found  in  many  other  organic  as  well  as 
inorganic  compounds.  The  different  chemic  elements  which  are  thus 
obtained,  and  the  percentage  in  which  they  exist  in  the  body,  are  as 
follows— viz.,  oxygen,  72  per  cent.;  hydrogen,  9.10  ;»nitrogen,  2.5  ;  carbon, 
I3-5°»  phosphorus,  1.15;  calcium,  1.30;  sulphur,  o.  147  ;  sodium,  o.  10; 
potassium,  0.026;  chlorin,  0.085;  fluorin,  iron  silicon,  magnesium,  in 
small  and  variable  amounts. 


THE  CARBOHYDRATES. 

The  carbohydrates  constitute  a  group  of  organic  bodies,  consisting 
mainly  of  starches  and  sugars,  having  their  origin  for  the  most  part  in  the 
vegetable  world.  In  many  respects  they  are  closely  related,  and  by  appro- 
priate  means   are   readily  converted   into  one  another.     In    composition 


CHEMIC  COMPOSITION  OF   THE   HUMAN    BODY.  17 

they  consist  of  the  elements  carbon,  hydrogen,  and  oxygen.  As  their 
name  implies,  the  hydrogen  and  oxygen  are  present  in  the  majority  of  these 
compounds  in  the  proportion  to  form  water,  or  as  2  :  I.  JThe  molecule  of 
the  carbohydrates  just  mentioned  consists  of  either  six  atoms  of  carbon  or  a 
multiple  of  six  ;  in  the  latter  case  the  quantity  of  hydrogen  and  oxygen 
taken  up  by  the  carbon  is  increased,  though  the  ratio  remains  unchanged. 

The  carbohydrates  may  be  divided  into  three  groups — viz.  :  (i)  Amy- 
loses,  including  starch,  dextrin,  glycogen,  and  cellulose;  (2)  dextroses, 
including  dextrose,  levulose,  galactose;  (3)  saccharoses,  including  saccha- 
rose, lactose,  and  maltose.  According  to  the  number  of  carbon  atoms 
entering  into  the  second  group  (six),  they  are  frequently  termed  mono- 
saccharids  ;  those  of  the  third  group,  disaccharids — twice  six  ;  those  of 
the  first  group,  polysaccharids — multiples  of  six. 

Though  but  few  of  the  members  of  the  carbohydrate  group  are  con- 
stituents of  the  human  body,  yet  on  account  of  their  importance  as  foods, 
and  their  relation  to  one  another,  a  few  of  their  chemic  features  will  be 
stated  in  this  connection. 

1.     AMYLOSES,  (C6H10OB)n. 

Starch  is  widely  distributed  in  the  vegetable  world,  being  abundant  in 
the  seeds  of  the  cereals,  leguminous  plants,  and  in  the  tubers  and  roots  of 
some  vegetables.  It  occurs  in  the  form  of  microscopic  granules,  which 
vary  in  size,  shape,  and  appearance,  according  to  the  plant  from  which  they 
are  obtained.  Each  granule  presents  a  nucleus,  or  hilum,  around  which  is 
arranged  a  series  of  eccentric  rings,  alternately  light  and  dark.  The 
granule  consists  of  an  envelope  and  stroma  of  cellulose,  containing  in  its 
meshes  the  true  starch  material — granulose.  Starch  is  insoluble  in  cold 
water  and  alcohol.  When  heated  with  water  up  to  700  C,  the  granules 
swell,  rupture,  and  liberate  the  granulose,  which  forms  an  apparent  solu- 
tion ;  if  present  in  sufficient  quantity,  it  forms  a  gelatinous  mass  termed 
starch  paste.  On  the  addition  of  iodin,  starch  strikes  a  characteristic  deep 
blue  color  ;  the  compound  formed — iodid  of  starch — is  weak,  and  the  color 
disappears  on  heating,  but  reappears  on  cooling. 

Boiling  starch  with  dilute  sulphuric  acid  (twenty-five  per  cent.)  converts 
it  into  dextrose.  In  the  presence  of  vegetable  diastase  or  animal  fer- 
ments, starch  is  converted  into  maltose  and  dextrose,  two  forms  of  sugar. 

Dextrin  is  a  substance  formed  as  an  intermediate  product  in  the  trans- 
formation of  starch  into  sugar.  There  are  at  least  two  principal  varieties — 
erythrodextrin,  which  strikes  a  red  color  with  iodin,  and  achro'odextrin, 


18  HUMAN   PHYSIOLOGY. 

which  is  without  color  when  treated  with  this  reagent.  In  the  pure  state 
dextrin  is  a  yellow- white  powder,  soluble  in  water.  In  the  presence  of 
animal  ferments  erythrodextrin  is  converted  into  maltose. 

Glycogen  is  a  constituent  of  the  animal  liver,  and,  to  a  slight  extent,  of 
muscles  and  of  tissues  generally.  In  the  tissues  of  the  embryo  it  is  espe- 
cially abundant.  When  obtained  in  a  pure  state  it  is  an  amorphous,  white 
powder.  It  is  soluble  in  water,  forming  an  opalescent  solution.  With 
iodin  it  strikes  a  port- wine  color.  In  some  respects  it  resembles  starch,  in 
others  dextrin.  Like  vegetable  starch,  glycogen  or  animal  starch  can  be 
converted  by  dilute  acids  and  ferments  into  sugar  (maltose). 

Cellulose  is  the  basis  material  of  the  more  or  less  solid  framework  of 
plants.  It  is  soluble  only  in  an  ammoniacal  solution  of  cupric  oxid,  from 
which  it  can  be  precipitated  by  acids.  It  is  an  amorphous  powder  ;  dilute 
acids  can  convert  it  into  dextrose. 

2.     DEXTROSES,  C6H1206. 

Dextrose,  glucose,  or  grape-sugar  is  found  in  grapes,  most  sweet 
fruits,  and  honey,  and  as  a  normal  constituent  of  liver,  blood,  muscles,  and 
other  animal  tissues.  In  the  disease  diabetes  mellitus  it  is  found  also  in 
the  urine. 

When  obtained  from  any  source,  it  is  soluble  in  water  and  in  hot  alcohol, 
from  which  it  crystallizes  in  six-sided  tables  or  prisms.  As  usually  met 
with,  it  is  in  the  form  of  irregular,  warty  masses.  It  is  sweet  to  the  taste  ; 
less  so,  however,  than  cane  sugar.  It  is  dextro-rotatory,  turning  the  plane 
of  polarized  light  to  the  right.  In  alkaline  solutions  dextrose  absorbs 
oxygen,  and  hence  in  the  presence  of  metallic  salts,  copper,  bismuth, 
silver,  etc.,  it  acts  as  a  reducing  agent.  On  this  property  the  various  tests 
for  dextrose,  as  well  as  other  sugars  which  have  the  same  property,  are 
based. 

Fehling's  Test. — The  solution  usually  employed  for  both  qualitative  and 
quantitative  purposes  is  a  solution  of  cupric  hydroxid  made  alkaline  by  an 
excess  of  sodium  or  potassium  hydroxid,  with  the  addition  of  sodium  and 
potassium  tartrate.  This  solution,  originally  suggested  by  Fehling,  bears 
his  name.  It  is  made  by  dissolving  cupric  sulphate  34.64  grams,  potas- 
sium hydroxid  125  grams,  sodium  and  potassium  tartrate  1 73  grams  in 
I  liter  of  distilled  water. 

The  reaction  is  expressed  by  the  following  equation  : 

CuSOi  +  2KOH  =  Cu(OH)2  +  K2S04. 


CHEMIC   COMPOSITION   OF  THE   HUMAN   BODY.  19 

The  object  of  the  sodium  and  potassium  tartrate  is  to  hold  the  Cu(OH)2 
in  solution.  If  a  few  cubic  centimeters  of  this  deep  blue  solution  be 
boiled  and  dextrose  then  added  and  the  solution  again  heated  to  the  boil- 
ing-point, the  cupric  hydroxid  is  reduced  to  the  condition  of  a  cuprous  oxid, 
which  shows  itself  as  a  red  or  orange-yellow  precipitate.  The  color  of  the 
precipitate  depends  on  the  relative  excess  of  either  copper  or  sugar,  being 
red  with  the  former,  orange  or  yellow  with  the  latter.  The  delicacy  of  this 
test  is  shown  by  the  fact  that  a  few  minims  of  this  solution  will  detect  in 
one  c.c.  of  water  the  y1^  of  a  milligram  of  sugar. 

For  quantitative  analysis,  ten  c.c.  of  Fehling's  solution,  diluted  with 
forty  c.c.  of  water,  are  heated  in  a  porcelain  capsule,  to  which  the  dextrose 
solution  is  cautiously  added  from  a  buret  until  the  blue  color  entirely 
disappears.  The  strength  of  this  solution  is  such  that  one  c.c.  is  decolor- 
ized by  five  milligrams  of  sugar,  from  which  the  percentage  of  sugar  in 
any  solution  can  be  determined. 

Fermentation  Test. — If  to  a  solution  of  dextrose  a  small  quantity  of  the 
yeast  plant  be  added,  and  the  solution  kept  at  a  temperature  of  250  C,  it 
will  gradually  undergo  fermentation  ;  that  is,  will  be  reduced  to  simpler 
compounds  and  especially  to  alcohol  and  carbon  dioxid.     The  change 
expressed  in  the  following  equation  : 

C6H1206  =  2C2H60  +  2C02 

Dextrose.  Alcohol.        Carbon 

Dioxid. 

About  ninety-five  per  cent,  of  the  dextrose  is  so  changed,  the  remaining 
five  per  cent,  yielding  secondary  products — succinic  acid,  glycerin,  etc. 

Levulose,  or  fruit-sugar,  is  found  in  association  with  dextrose  as  a 
constituent  of  many  fruits.  It  is  sweeter  than  dextrose  and  more  soluble 
in  both  water  and  dilute  alcohol.  From  alcoholic  solutions  it  crystallizes 
in  fine,  silky  needles,  though  it  usually  occurs  in  the  form  of  a  syrup. 

Levulose  is  distinguished  from  dextrose  by  its  property  of  turning  the 
plane  of  polarized  light  to  the  left ;  the  extent  to  which  it  does  so,  how- 
ever, varies  with  the  temperature  and  concentration  of  the  solution. 

Under  the  influence  of  the  yeast  plant  it  slowly  undergoes  fermentation, 
yielding  the  same  products  as  dextrose.  It  also  has  a  reducing  action  on 
cupric  oxid. 

Galactose  is  obtained  by  boiling  milk- sugar  (lactose)  with  dilute  sul- 
phuric acid.  In  many  chemic  relations  it  resembles  dextrose.  It  is  less 
soluble  in  water,  however,  crystallizes  more  easily,  and  has  a  greater  dex- 
tro-rotatory power.     It  also  undergoes  fermentation  with  the  yeast  plant. 


20  HUMAN    PHYSIOLOGY. 

3.  SACCHAROSES,  CxaHnOxa. 

Saccharose,  or  cane-sugar,  is  widely  distributed  throughout  the  vege- 
table world,  but  is  especially  abundant  in  sugar-cane,  sorghum  cane,  sugar- 
beet,  Indian  corn,  etc.  It  crystallizes  in  large  monoclinic  prisms.  It  is 
soluble  in  water  and  in  dilute  alcohol.  Saccharose  has  no  reducing  power 
on  cupric  oxid,  and  hence  its  presence  can  not  be  detected  by  Fehling's 
solution.  It  is  dextro-rotatory.  Boiled  with  dilute  mineral,  as  well  as 
organic  acids,  saccharose  combines  with  water,  and  undergoes  some  change 
in  virtue  of  which  it  rotates  the  plane  of  polarized  light  to  the  left,  and  hence 
the  product  is  termed  invert  sugar.  This  latter  has  been  shown  to  be  a 
mixture  of  equal  quantities  of  levulose  and  dextrose.  This  inversion  of 
saccharose  through  hydration  and  decomposition  is  expressed  by  the  follow- 
ing equation  : 

C12H22011  +  H20  =  C6H1206  +  C6H1206 
Saccharose.      Water.       Levulose.  Dextrose. 


invert  Sugar. 

Saccharose  is  not  directly  fermentable  by  yeast,  but  through  the  specific 
action  of  a  ferment,  invertin  or  invertase,  secreted  by  the  yeast  plant,  or  the 
inverting  ferment  of  the  small  intestine,  it  undergoes  inversion,  as  pre- 
viously stated,  after  which  it  is  readily  fermented,  yielding  alcohol  and 
carbon  dioxid. 

Lactose  is  the  form  of  sugar  found  exclusively  in  the  milk  of  the  mam- 
malia, from  which  it  can  be  obtained  in  the  form  of  hard,  white,  rhombic 
prisms  united  with  one  molecule  of  water.  It  is  soluble  in  water,  insol- 
uble in  alcohol  and  ether.  It  is  dextro-rotatory.  It  reduces  cupric  oxid, 
but  to  a  less  extent  than  dextrose.  Dilute  acids  decompose  it  into  equal 
quantities  of  dextrose  and  galactose.  Lactose  is  not  fermentable  with 
yeast,  but  in  the  presence  of  the  lactic  acid  bacillus  it  is  decomposed  into 
lactic  acid,  and  finally  into  butyric  acid,  as  follows  : 
C12H22Ou  +  H20=4C3H603 

Lactose.         Water.     Lactic  Acid. 

2C,H603    =     C4H802     +     2C02     -f     2H2 

Lactic  Acid.  Butyric  Acid.  Carbon  Free 

Dioxid.  Hydrogen. 

Maltose  is  a  transformation  product  of  starch,  and  arises  whenever  the 
latter  is  acted  on  by  malt  extract  or  the  diastatic  ferments  in  saliva  and 
pancreatic  juice.  It  can  also  be  produced  by  the  action  of  dilute  sulphuric 
acid  on  starch.     The  change  is  expressed  by  the  following  equation  : 

2C6H10O6-f  H20  =  C12H22On 

Starch.         Water.  Maltose. 


CHEMIC   COMPOSITION    OF   THE    HUMAN   BODY.  21 

Maltose  crystallizes  in  the  form  of  white  needles,  which  are  soluble  in 
water  and  in  dilute  alcohol.  It  is  dextro-rotatory.  In  the  presence  of 
ferments  and  dilute  acids  maltose  undergoes  hydration  and  decomposition, 
giving  rise  to  two  molecules  of  dextrose.  It  has  a  reducing  action  on 
cupric  oxid.  Fermentation  is  readily  caused  by  yeast,  but  whether 
directly  or  indirectly  by  inversion  is  somewhat  uncertain. 

Osazones. — All  the  sugars  which  possess  the  power  of  reducing  cupric 
oxid  are  capable  of  combining  with  phenyl-hydrazin,  with  the  formation 
of  compounds  termed  osazones.  The  osazones  so  formed  are  crystalline 
in  structure,  but  have  different  melting-points,  varying  degrees  of  solubility 
and  optic  properties,  all  of  which  serve  to  detect  the  various  sugars  and 
to  distinguish  one  from  the  other.  Of  the  different  osazones,  phenyl -gluco- 
sazone  is  the  most  characteristic,  and  occurs  in  the  form  of  long,  yellow 
needles.  It  may  be  obtained  from  dextrose  by  the  following  method  :  To 
fifty  c.c.  of  a  dextrose  solution  add  two  gm.  of  phenyl-hydrazin  and  two 
gm.  of  sodium  acetate,  and  boil  for  an  hour.  On  cooling,  the  osazone 
crystallizes  in  the  form  of  long,  yellow  needles. 

THE  FATS. 

The  fats  constitute  a  group  of  organic  bodies  found  in  the  tissues  of  both 
vegetables  and  animals.  In  the  vegetable  world  they  are  largely  found  in 
fruits,  seeds,  and  nuts,  where  they  probably  originate  from  a  transformation 
of  the  carbohydrates.  In  the  animal  body  the  fats  are  found  largely  in 
the  subcutaneous  tissue,  in  the  marrow  of  bones,  in  and  around  various 
internal  organs  and  in  milk.  In  these  situations  fat  is  contained  in  small, 
round  or  polygon-shaped  vesicles,  which  are  united  by  areolar  tissue  and 
surrounded  by  blood-vessels.  At  the  temperature  of  the  body  the  fat  is 
liquid,  but  after  death  it  soon  solidifies  from  the  loss  of  heat. 

The  fats  are  compounds  consisting  of  carbon,  hydrogen,  and  oxygen,  of 
which  the  first  is  the  chief  ingredient,  forming  by  weight  about  seventy-five 
per  cent.,  while  the  last  is  present  only  in  small  quantity.  The  fat,  as 
found  in  animals,  is  a  mixture,  in  varying  proportions  in  different  animals, 
of  three  neutral  fats — stearin,  palmitin,  and  olein.  Each  fat  is  a  derivative 
of  glycerin  and  the  particular  acid  indicated  by  its  name — e.  g.,  stearic 
acid,  in  the  case  of  stearin,  etc.  The  reaction  which  takes  place  in  the 
combination  of  glycerin  and  the  acid  is  expressed  in  the  following  equation  : 

C3H5(HO)3  +  (HC18H3502)3  =  C3H5(C18H3502)3  +  3H20. 
Glycerin.  Stearic  Acid.  Stearin,  Water, 


22  HUMAN   PHYSIOLOGY. 

Hence,  strictly  speaking,  the  fats  are  compound  ethers,  in  which  the 
hydrogen  of  the  organic  acid  is  replaced  by  the  trivalent  radicle,  tritenyl, 

C3H5' 

Stearin,  C3H5(C18H3502)3,  is  the  chief  constituent  of  the  more  solid 
fats.  It  is  solid  at  ordinary  temperatures,  melting  at  55 °  C,  then  solidify- 
ing again  as  the  temperature  rises,  until  at  Jl°  C.  it  melts  permanently. 
It  crystallizes  in  square  tables. 

Palmitin,  C3H5(C16H3102)3,  is  a  semifluid  fat,  solid  at  450  C.  and  melt- 
ing at  620  C.     It  crystallizes  in  fine  needles,  and  is  soluble  in  ether. 

Olein,  C3H5(C]8H3302)3,  is  a  colorless,  transparent  fluid,  liquid  at  ordi- 
nary temperatures,  only  solidifying  at  o°  C.  It  possesses  marked  solvent 
powers,  and  holds  stearin  and  palmitin  in  solution  at  the  temperature  of 
the  body. 

Saponification. — When  subjected  to  the  action  of  superheated  steam, 
a  neutral  fat  is  saponified — i.  e.,  decomposed  into  glycerin  and  the  particu- 
lar acid  indicated  by  the  name  of  the  fat  used  :  e.  g.,  stearic,  palmitic,  or 
oleic.     The  reaction  is  expressed  as  follows  : 

C3H5(C18H3302)3  +  3H20  =  C3H5(  HO)3  +  3(  C18H3,Oa) 

Olein.  Water.  Glycerin.  Oleic  Acid. 

The  fatty  acids  thus  obtained  are  characterized  by  certain  chemic  features, 
as  follows : 

Stearic  acid  is  a  firm,  white  solid,  fusible  at  690  C.  It  is  soluble  in 
ether  and  alcohol,  but  not  in  water. 

Palmitic  acid  occurs  in  the  form  of  white,  glistening  scales  or  needles, 
melting  at  620  C. 

Oleic  acid  is  a  clear,  colorless  liquid,  tasteless  and  odorless  when  pure. 
It  crystallizes  in  white  needles  at  o°  C. 

If  this  saponification  take  place  in  the  presence  of  an  alkali, — e.  g., 
potassium  hydroxid,  sodium  hydroxid, — the  acid  produced  combines  at 
once  with  the  alkali  to  form  a  salt  known  as  a  soap,  while  the  glycerin 
remains  in  solution.     The  reaction  is  as  follows  : 

3KHO  +  (C18H3402)3  -  3(KC18HSS02)  +  C3H5(HO)3 

Potassium.         Oleic  Acid.         Potassium  Oleate.  Glycerin. 

All  soaps  are,  therefore,  salts  formed  by  the  union  of  alkalies  and  fatty 
acids.  The  sodium  soaps  are  generally  hard,  while  the  potassium  soaps 
are  soft.  Those  made  with  stearin  and  palmitin  are  harder  than  those 
made  with  olein.  If  the  soap  is  composed  of  lead,  zinc,  copper,  etc.,  it 
is  insoluble  in  water. 


CHEMIC   COMPOSITION    OF  THE   HUMAN    BODY.  23 

Emulcification. — When  a  neutral  oil  is  vigorously  shaken  with  water 
or  other  fluid,  it  is  broken  up  into  minute  globules  that  are  more  or  less 
permanently  suspended ;  the  permanency  depending  on  the  nature  of  the 
liquid.  The  most  permanent  emulsions  are  those  made  with  soap  solu- 
tions. The  process  of  emulsiflcation  and  the  part  played  by  soap,  can  be 
readily  observed  by  placing  on  a  few  cubic  centimeters  of  a  solution  of 
sodium  carbonate  o.  25  per  cent,  of  a  small  quantity  of  a  perfectly  neutral 
oil  to  which  has  been  added  2  or  3  per  cent,  of  a  fatty  acid.  The  combi- 
nation of  the  acid  and  the  alkali  at  once  forms  a  soap.  The  energy  set 
free  by  this  combination  rapidly  divides  up  the  oil  into  extremely  minute 
globules.     A  spontaneous  emulsion  is  thus  formed. 

In  addition  to  the  ordinary  fats,  there  are  present  in  different  tissues 
several  compounds  which,  though  usually  regarded  as  fats,  nevertheless 
differ  materially  from  them  in  composition,  containing,  as  they  do,  both 
nitrogen  and  phosphorus.  These  nitrogenized  or  phosphorized  fats  are  as 
follows  : 

Lecithin,  CwH90N.PO9,  is  found  in  blood,  lymph,  red  and  white  cor- 
puscles, nerve  tissue,  yolk  of  eggs,  etc.  When  pure,  it  presents  itself 
generally  under  the  form  of  a  white,  crystalline  powder,  though  some- 
times as  a  white,  waxy  mass.  Lecithin  is  easily  decomposed,  yielding, 
with  various  reagents,  glycero-phosphoric  acid,  cholin  and  stearic  acid. 

Protagon,  C1G0H308N5PO35,  is  found  most  abundantly  in  the  brain  tissue, 
especially  in  the  white  portion.  It  crystallizes  from  warm  alcoholic  solu- 
tions, on  cooling,  in  the  form  of  white  needles,  generally  arranged  in  groups. 
It  melts  at  2000  C,  and  forms  a  syrupy  liquid. 

Cerebrin,  C17H33N.03,  is  found  largely  in  the  brain,  in  nerves,  and  in 
pus-corpuscles.  It  is  a  soft,  white,  amorphous  powder,  insoluble  in  water, 
but  swelling  up  like  starch  in  boiling  water.  When  boiled  with  dilute 
acids,  it  is  decomposed,  yielding  a  fermentable  dextro-rotatory  sugar,  iden- 
tical with  galactose.      Cerebrin  may,  therefore,  be  regarded  as  a  glucosid. 

THE  PROTEIDS. 

The  proteids  constitute  a  group  of  organic  bodies  which  are  found  in 
both  vegetable  and  animal  tissues.  Though  present  in  all  animal  tissues, 
they  are  especially  abundant  in  muscles  and  bones,  where  they  constitute 
twenty  per  cent,  and  thirty  per  cent,  respectively.  Though  genetically  re- 
lated, and  possessing  many  features  in  common,  the  different  members  of 
the  proteid  group  are  distinguished  by  characteristic  physical  and  chemic 
properties. 


24  HUMAN    PHYSIOLOGY. 

The  average  percentage  composition  of  several  proteids  is  shown  in  the 
following  analyses  : 

C.       H.         N.         O.  S. 

Egg-albumin,   .  52.9     7.2     15. 6     23.9  0.4    ( Wurtz). 

Serum-albumin,  53.0     6.8     16.0     22.29  1-77  (Hammersten). 

Casein,.    .    .    .53.3     7.07  15.91   22.03  0.82  (Chittenden  and    Painter). 

Myosin,     .    .    .52.82  7.  II    16.77  21.90  1. 27  (Chittenden  and  Cummins). 

The  molecular  composition  of  the  proteids  is  not  definitely  known,  and 
the  formulae  which  have  been  suggested  are  therefore  only  approximative. 
Leow  assigns  to  albumin  the  formula  C72HU2N18022S,  while  Schutzen- 
berger  raises  the  numbers  to  C240H392N65O75S3,  either  of  which  shows  that 
the  proteid  molecule  is  extremely  complex.  As  a  class,  the  proteids  are 
characterized  by  the  following  properties  : 

1.  Indiffusibility. — None  of  the  proteids  normally  assumes  the  crystalline 
form,  and  hence  they  are  not  capable  of  diffusing  through  parchment  or 
an  animal  membrane.  Peptone,  a  product  of  the  digestion  of  proteids,  is 
an  exception  as  regards  its  diffusibility.  As  met  with  in  the  body,  all 
proteids  are  amorphous,  but  vary  in  consistence  from  the  liquid  to  the 
solid  state.  The  colloid  character  of  the  proteids  permits  of  their  sepa- 
ration and  purification  from  crystalloid  diffusible  compounds  oy  the  proc- 
ess of  dialysis. 

2.  Solubility. — Some  of  the  proteids  are  soluble  in  water,  others  in  solu- 
tions of  the  neutral  salts  of  varying  degrees  of  concentration,  in  strong 
acids  and  alkalies.     All  are  insoluble  in  alcohol  and  ether. 

3.  Coagulability. — Under  the  influence  of  heat  and  various  acids  and 
animal  ferments,  the  proteids  readily  pass  from  the  soluble  liquid  state 
to  the  insoluble  solid  state,  attended  by  a  permanent  alteration  in  their 
chemic  composition.  To  this  change  the  term  coagulation  has  been 
given.  The  various  proteids  not  only  coagulate  at  different  tempera- 
tures, but  with  different  chemic  reagents — distinctive  features  which 
permit  not  only  of  their  detection,  but  separation.  Proteids  are  capable 
of  precipitation  without  losing  their  solubility  by  ammonium  sulphate, 
sodium  chlorid  and  magnesium  sulphate. 

4.  Fermentability. — In  the  presence  of  specific  microorganisms — bac- 
teria— the  proteids,  owing  to  their  complexity  and  instability,  are  prone 
to  undergo  disintegration  and  reduction  to  simpler  compounds.  This 
decomposition  or  putrefaction  occurs  most  readily  when  the  conditions 
most  favorable  to  the  growth  of  bacteria  are  present— Mz. ,  a  temperature 
varying  from  250  C.  to  4QP  C,  moisture  and  oxygen.     The  intermediate 


CHEMIC   COMPOSITION    OF   THE   HUMAN    BODY.  25 

as  well  as  the  terminal  products  of  the  decomposition  of  the  proteids  are 
numerous,  and  vary  with  the  composition  of  the  proteid  and  the  specific 
physiologic  action  of  the  bacteria.  Among  the  intermediate  products 
is  a  series  of  alkaloid  bodies,  some  of  which  possess  marked  toxic 
properties,  known  as  ptomains  or  toxins.  The  toxic  symptoms  which 
frequently  follow  the  ingestion  of  foods  in  various  stages  of  putre- 
faction are  to  be  attributed  to  these  compounds.  The  terminal  products 
are  represented  by  hydrogen  sulphid,  ammonia,  carbon  dioxid,  fats, 
phosphates,  nitrates,  etc. 

Color  Tests  for  Proteids. — When  proteids  are  present  in  solution, 
they  may  be  detected  by  the  following  color  reactions — viz.  : 

1.  Xanthoproteic.  The  solution  is  boiled  with  nitric  acid  for  several 
minutes,  when  the  proteid  assumes  a  light  yellow  color.  After  the 
solution  has  cooled,  the  addition  of  ammonia  changes  the  color  to  an 
orange  or  amber-red. 

2.  The  rose-red  reaction.  The  solution  is  boiled  with  acid  nitrate  of 
mercury  (Millon's  reagent)  for  a  few  minutes,  when  the  coagulated  pro- 
teid turns  a  purple -red  color. 

3.  The  blue-violet  reaction.  A  few  drops  of  copper  sulphate  solution  are 
first  added  to  the  proteid  solution,  and  then  an  excess  of  sodium  hydroxid. 
A  blue-violet  color  is  produced,  which  deepens  somewhat  on  heating, 
but  no  further  change  ensues. 

The  proteids  found  in  the  animal  body,  though  possessing  many  features 
in  common,  are  nevertheless  characterized  by  certain  special  features 
which  not  only  serve  for  their  identification,  but  for  their  classification  into 
well-defined  groups,  as  follows  : 

1.  NATIVE  PROTEIDS. 

The  members  of  this  group  are  soluble  in  water,  in  dilute  saline  solutions, 
and  in  saturated   solutions  of  sodium  chlorid   and   magnesium  sulphate. 
They  are  coagulated  by  heat,  and  when  dried  form  an  amber-colored  mass. 
(a)  Serum-albumin  is  found  in  blood,  lymph,  chyle,  tissue  fluids, 
and  milk.     It  is  obtained  readily  by  precipitation  from  blood-serum, 
after  the  other  proteids  have  been  removed,  on  the  addition  of  am- 
monium sulphate.     When  freed  from  saline  constituents,  it  presents 
itself  as  a  pale,  amorphous  substance,  soluble  in  water  and  in  strong 
nitric  acid.     It  is  coagulated  at  a  temperature  of  730  C,  as  well  as 
by  various  acids — e.  g.,  citric,  picric,  nitric,  etc.       It  has  a  rotatory 
power  of — 62. 6°. 
3 


26  HUMAN    PHYSIOLOGY. 

(£)  Egg -albumin. — Though  not  a  constituent  of  the  human  body, 
egg- albumin  resembles  the  foregoing  in  many  respects.  When  ob- 
tained in  the  solid  form  from  the  white  of  the  egg,  it  is  a  yellow  mass 
without  taste  or  odor.  Though  similar  to  serum-albumin,  it  differs 
from  it  in  being  precipitated  by  ether,  in  coagulating  at  540  C. ,  and 
in  having  a  lower  rotatory  power,  — 35 .5°. 

2.  GLOBULINS. 

The  rhembers  of  this  group  are  insoluble  in  water  and  in  saturated  solu- 
tions of  sodium  chlorid  and  magnesium  sulphate  and  ammonium  sulphate. 
They  are  soluble,  however,  in  dilute  saline  solutions — e.  g.,  sodium  chlorid 
(one  per  cent. ),  potassium  chlorid,  ammonium  chlorid,  etc.  They  are 
coagulated  by  heat. 

[a)  Serum-globulin  or  Paraglobulin. — This  proteid,  as  its  name 
implies,  is  found  in  blood-serum,  though  it  is  present  in  other  animal 
fluids.  When  precipitated  by  magnesium  sulphate  or  carbon  dioxid, 
it  presents  itself  as  a  flocculent  substance,  insoluble  in  water,  solu- 
ble in  dilute  acids  and  alkalies,  and  coagulating  at  750  C. 
(3)  Fibrinogen. — This  proteid  is  found  in  blood  plasma  in  association 
with  serum-globulin  and  serum-albumin.  It  is  also  present  in 
lymph-tissue  fluids  and  in  pathologic  transudates.  It  can  be 
obtained  from  blood -plasma  which  has  been  previously  treated  with 
magnesium  sulphate  on  the  addition  of  a  saturated  solution  of  sodium 
chlorid.  It  is  soluble  in  dilute  acids  and  alkalies,  and  coagulates  at 
56°  C. 
(c)  Myosinogen. — This  proteid  is  a  constituent  of  the  protoplasm  of 
the  muscle-fibers.  During  the  living  condition  it  is  liquid,  but  after 
death  it  i-eadily  undergoes  decomposition  into  an  insoluble  portion 
known  as  myosin  and  a  soluble  albumin.  It  is  soluble  in  dilute 
hydrochloric  acid  and  dilute  alkalies.  It  coagulates  at  560  C. 
(</)  Globin. — This  is  a  product  of  the  spontaneous  decomposition  of 
the  coloring  matter  of  the  blood, — hemoglobin, — and  arises  when 
the  latter  is  exposed  to  the  air. 
(<?)  Crystallin  or  Globulin. — This  is  obtained  by  passing  a  stream 
of  CO.;  through  a  watery  extract  of  the  crystalline  lens. 

3.  DERIVED  ALBUMINS  OR  ALBUMINATES. 

The  proteids  of  this  group  are  derived  from  both  native  albumins  and 
globulins  by  the  gradual  action  of  dilute  acids  and  alkalies,  and  may  be 
regarded  as  compounds  of  a  proteid  with  an  acid  or  an  alkali. 


CHEMIC   COMPOSITION    OF   THE    HUMAN   BODY.  27 

(a)  Acid-albumin. — This  is  formed  when  a  native  albumin  is 
digested  with  dilute  hydrochloric  acid  (0.2  per  cent.)  or  dilute  sul- 
phuric acid  for  some  minutes.  It  is  precipitated  by  neutralization 
with  sodium  hydroxid  (0. 1  per  cent,  solution).  After  the  precipi- 
tate is  washed,  it  is  found  to  be  insoluble  in  distilled  water  and  in 
neutral  saline  solutions.  In  acid  solutions  it  is  not  coagulated  by 
heat. 

(6)  Alkali-albumin. — This  is  formed  when  a  native  albumin  is  treated 
with  a  dilute  alkali — e.  g.,  0. 1  per  cent,  of  sodium  hydroxid — for 
five  or  ten  minutes.  On  careful  neutralization  with  dilute  hydro- 
chloric acid,  it  is  precipitated.  It  is  also  insoluble  in  distilled  water 
and  in  alkaline  solutions ;  it  is  not  coagulable  by  heat. 

(<r)  Caseinogen. — This  is  the  principal  proteid  of  milk,  in  which  it  ex- 
ists in  association  with  an  alkali,  and  hence  was  formerly  regarded 
as  a  native  alkali-albumin.  It  is  precipitated  by  acetic  acid  and  by 
magnesium  sulphate.  It  is  coagulated  by  rennet — that  is,  separated 
into  an  insoluble  proteid,  casein  or  tyrein,  and  a  soluble  albumin. 
Calcium  phosphate  seems  to  be  the  alkali  necessary  to  this  process, 
for  if  it  be  removed  by' dialysis,  or  precipitated  by  the  addition  of 
potassium  oxalate,  coagulation  does  not  take  place. 

4.    COAGULATED  PROTEIDS. 

Although  these  proteids  are  not  found  as  constituents  of  the  animal 
organism,  they  possess  much  interest  on  account  of  their  relation  to  prepared 
foods  and  to  the  digestive  process.  They  are  produced  when  solutions  of 
egg-albumin,  serum-albumin,  or  globulins  are  subjected  to  a  temperature  of 
1000  C.  or  to  the  prolonged  action  of  alcohol.  They  are  insoluble  in  water, 
in  dilute  acids,  and  in  neutral  saline  solutions.  In  this  same  group  may  be 
included  also  those  coagulated  proteid's  which  are  produced  by  the  action 
of  animal  ferments  on  soluble  proteids  -  <?.  g. ,  fibrin,  myosin,  casein. 

Fibrin. — Fibrin  is  derived  from  a  soluble  proteid — fibrinogen — by 
the  action  of  a  special  ferment.  It  is  not  present  under  normal  cir- 
cumstances in  the  circulating  blood,  but  makes  its  appearance  after 
the  blood  is  withdrawn  from  the  vessels  and  at  the  time  of  coagu- 
lation. It  can  also  be  obtained  by  whipping  the  blood  with  a 
bundle  of  twigs,  on  which  it  accumulates.  When  freed  from  blood 
by  washing  under  water,  it  is  seen  to  consist  of  bundles  of  white 
elastic  fibers  or  threads.  It  is  insoluble  in  water,  in  alcohol,  and 
ether.     In  dilute  acids  it  swells,  becomes  transparent,  and  finally  is 


28  HUMAN  PHYSIOLOGY. 

converted  into  acid-albumin.  In  dilute  alkalies  a  similar  change  takes 
place,  but  the  resulting  product  is  an  alkali-albumin.  Fibrin  possesses 
the  property  of  decomposing  hydrogen  dioxid,  H202 — i.  <?.,  liberat- 
ing oxygen,  which  accumulates  in  the  form  of  bubbles  on  the  fibrin. 
On  incineration  fibrin  yields  an  ash  which  contains  calcium  phos- 
phate and  magnesium  phosphate. 

5.  PROTEOSES  AND  PEPTONES. 

During  the  progress  of  the  digestive  process,  as  it  takes  place  in  the 
stomach  and  intestines,  there  is  produced  by  the  action  of  the  gastric  and 
pancreatic  juices,  out  of  the  proteids  of  the  food,  a  series  of  new  proteids, 
known  as  proteoses  and  peptones.  The  chemic  properties  of  these  sub- 
stances will  be  considered  in  connection  with  the  process  of  digestion. 

6.  ALBUMINOIDS. 

The  albuminoids  constitute  a  group  of  substances  similar  to  the  proteids 
in  many  respects,  though  differing  from  them  in  others.  When  obtained 
from  the  tissues,  in  which  they  form  an  organic  basis,  they  are  found  to  be 
amorphous,  colloid,  and  when  decomposed  yield  products  similar  to  those 
of  the  true  proteids.     The  principal  members  of  this  group  are  as  follows  : 

(«)  Mucin. — This  is  the  viscid,  tenacious  constituent  of  mucus 
secreted  by  the  epithelial  cells  of  mucous  membranes.  It  is  also 
present  in  the  intercellular  substance  of  the  connective  tissue.  It  is 
readily  precipitated  by  acetic  acid. 

(b)  Collagen,  Ossein. — These  are  two  closely  allied,  if  not  identical, 
substances,  found  respectively  in  the  white  fibrous  connective  tissue 
and  in  bone.  When  the  tendons  of  muscles,  the  ligaments,  or  de- 
calcified bone  are  boiled  for  several  hours,  the  collagen  and  ossein 
are  converted  into  soluble  gelatin,  which,  when  the  solution  cools, 
becomes  solid. 

(c)  Chondrinigen. — This  is  supposed  to  be  the  organic  basis  of  the 
more  permanent  cartilages.  When  they  are  boiled,  they  yield  a 
substance  which  gelatinizes  on  cooling,  and  to  which  the  name 
chondrin  has  been  given. 

(d )  Elastin  is  the  name  given  to  the  substance  composing  the  fibers 
of  the  yellow,  elastic  connective  tissue. 

(<?)  Keratin  is  the  substance  found  in  all  horny  and  epidermic  tissues, 
such  as  hairs,  nails,  scales,  etc.  It  differs  from  most  proteids  in 
containing^a  high  percentage  of  sulphur. 


CHEMIC  COMPOSITION   OF   THE  HUMAN  BODY.  29 

{/)  Nuclein. — This  is  an  amorphous  substance  obtained  from  the 
nuclei  of  both  animal  and  vegetable  cells.  The  chief  constituent 
appears  to  be  nucleic  acid.  Chemic  analysis  shows  that  nuclein 
contains  not  less  than  three  per  cent,  of  phosphorus.  On  boiling 
with  strong  alkalies,  nuclein  is  partially  decomposed,  yielding  a 
proteid  resembling  globulin  and  phosphoric  acid.  A  nucleo- 
proteid  is  a  compound  of  nuclein  and  a  proteid. 

INORGANIC  CONSTITUENTS. 

The  inorganic  compounds  and  mineral  constituents  obtained  from  the 
solids  and  fluids  of  the  body  are  very  numerous,  and,  in  some  instances, 
quite  abundant.  Though  many  of  trie  compounds  thus  obtained  are  un- 
doubtedly derivatives  of  the  tissues  and  necessary  to  their  physical  and 
physiologic  activity,  others,  in  all  probability,  are  decomposition  products, 
or  transitory  constituents  introduced  with  the  food.  Of  the  inorganic  com- 
pounds, the  following  are  the  most  important : 

WATER. 

Water  is  the  most  important  of  the  inorganic  constituents,  as  it  is  indis- 
pensable to  life.  It  is  present  in  all  the  tissues  and  fluids  without  exception, 
varying  from  99  per  cent,  in  the  saliva  to  80  per  cent,  in  the  blood,  75 
per  cent,  in  the  muscles  to  2  per  cent,  in  the  enamel  of  the  teeth.  The 
total  quantity  contained  in  a  body  weighing  75  kilograms  (165  pounds) 
is  52.5  kilograms  (115  pounds).  Much  of  the  water  exists  in  a  free 
condition,  and  forms  the  chief  part  of  the  fluids,  giving  to  them  their 
characteristic  degree  of  fluidity.  Possessing  the  capability  of  holding  in 
solution  a  large  number  of  inorganic  as  well  as  some  organic  compounds, 
and  being  at  the  same  time  diffusible,  it  renders  an  interchange  of  mate- 
rials between  all  portions  of  the  body  possible.  It  aids  in  the  absorption 
of  new  material  into  the  blood  and  tissues,  and  at  the  same  time  it  trans- 
fers waste  products  from  the  tissues  to  the  blood,  from  which  they  are 
finally  eliminated,  along  with  the  water  in  which  they  are  dissolved.  A 
portion  of  the  water  is  chemically  combined  with  other  tissue  constituents, 
and  gives  to  the  tissues  their  characteristic  physical  properties.  The  con- 
sistency, elasticity,  and  pliability  are,  to  a  large  extent,  conditioned  by  the 
amount  of  water  they  contain.  The  total  quantity  of  water  eliminated  by 
the  kidneys,  lungs,  and  skin  amounts  to  about  three  kilograms  (6}4 
pounds). 


30  HUMAN   PHYSIOLOGY. 

CALCIUM  COMPOUNDS. 

Calcium  phosphate,  Ca3(P04)2,  has  a  very  extensive  distribution 
throughout  the  body.  It  exists  largely  in  the  bones,  teeth,  and  to  a  slight 
extent  in  cartilage,  blood,  and  other  tissues.  Milk  contains  0.27  per  cent. 
The  solidity  of  the  bones  and  teeth  is  almost  entirely  due  to  the  presence  of 
this  salt,  and  is,  therefore,  to  be  regarded  as  necessary  to  their  structure. 
It  enters  into  chemic  union  with  the  organic  matter,  as  shown  by  the 
fact  that  it  can  not  be  separated  from  it  except  by  chemic  means,  such  as 
hydrochloric  acid.  Though  insoluble  in  water,  it  is  held  in  solution  in  the 
blood  and  milk  by  the  proteid  constituents,  and  in  the  urine  by  the  acid 
phosphate  of  soda.  The  total  quantity  of  calcium  phosphate  which  enters 
into  the  formation  of  the  body  has  been  estimated  at  2.5  kilograms.  The 
amount  eliminated  daily  from  the  body  has  been  estimated  at  0.4  gm.,  a 
fact  which  indicates  that  nutritive  changes  do  not  take  place  with  much 
rapidity  in  those  tissues  in  which  it  is  contained. 

Calcium  carbonate,  CaC03,  is  present  in  practically  the  same  situations 
in  the  body  as  the  phosphate,  and  plays  essentially  the  same  role.  It  is, 
however,  found  in  the  crystalline  form,  aggregated  in  small  masses  in  the 
internal  ear,  forming  the  otoliths,  or  ear  stones.  Though  insolable,  it  is 
held  in  solution  by  the  carbonic  acid  diffused  through  the  fluids. 

Calcium  fiuorid,  CaF2,  is  found  in  bones  and  teeth. 

SODIUM  COMPOUNDS. 

Sodium  chlorid,  NaCl,  is  present  in  all  the  tissues  and  fluids  of  the  body, 
but  especially  in  the  blood,  0.6  per  cent.,  lymph,' 0.5,  and  pancreatic  juice, 
o.  25  per  cent.  The  entire  quantity  in  the  body  has  been  estimated  at  about 
200  gm.  Sodium  chlorid  is  of  much  importance  in  the  body,  as  it  deter- 
mines and  regulates  to  a  large  extent  the  phenomena  of  diffusion  which 
are  there  constantly  taking  place.  This  is  illustrated  by  the  fact  that  a 
solution  of  albumin  placed  in  the  rectum  without  the  addition  of  this  salt 
will  not  be  absorbed.  When  the  salt  is  added,  absorption  takes  place. 
The  ingested  water  is  absorbed  into  the  blood  largely  in  consequence  of 
the  percentage  of  this  salt  which  it  contains.  The  normal  percentage  of 
sodium  chlorid  in  the  blood-plasma  assists  in  maintaining  the  shape  and 
structure  of  the  red  blood- corpuscles  by  determining  the  amount  of  water 
entering  into  their  composition.     The  same  is  true  of  other  tissue  elements. 

Sodium  chlorid  also  influences  the  general  nutritive  process,  increasing 
the  disintegration  of  the  proteids,  as  shown  by  the  increased  amount  of 
urea  excreted.     During  its  existence  in  the  body  it  undergoes  some  chemic 


CHEMIC   COMPOSITION    OF  THE   HUMAN   BODY.  31 

transformations  or  decompositions,  yielding  its  chlorid  to  form  potassium 
chlorid  of  the  blood-corpuscles  and  muscles  and  to  form  the  hydrochloric 
acid  of  the  gastric  juice. 

Sodium  phosphate,  Na2IIP04,  is  found  in  all  solids  and  fluids  of  the 
body,  to  which,  with  but  few  exceptions,  it  imparts  an  alkaline  reaction. 
This  is  especially  true  of  blood,  lymph,  and  tissue  fluids  generally.  It  is 
essential  to  physiologic  action  that  all  tissue  elements  should  be  bathed  by 
an  alkaline  medium. 

Sodium  carbonate,  Na2C03,  is  generally  found  in  association  with  the 
preceding  salt.  As  it  is  also  an  alkaline  compound,  it  assists  in  giving  to 
the  blood  and  lymph  their  characteristic  alkalinity.  In  carnivorous  ani- 
mals the  sodium  phosphate  is  the  more  abundant,  while  in  the  herbivorous 
animals  the  reverse  is  true. 

Sodium  sulphate,  Na2S04,  is  present  in  many  of  the  tissues  and  fluids, 
especially  the  urine.  Though  introduced  in  the  food,  it  is  also,  in  all 
probability,  formed  in  the  body  from  the  decomposition  and  oxidation  of 
the  proteids. 

POTASSIUM  COMPOUNDS. 

Potassium  chlorid,  KC1,  is  met  with  in  association  with  sodium  chlorid 
in  almost  all  situations  in  the  body.  It  preponderates,  however,  in  the 
tissue  elements,  especially  in  the  muscle  tissue,  nerve  tissue,  and  red  cor- 
puscles. The  plasma  with  which  these  structures  are  bathed  contains  but 
a  very  small  amount  of  this  salt,  but,  as  previously  stated,  a  relatively  large 
quantity  of  sodium  chlorid.  Though  introduced  to  some  extent  in  the 
food,  it  is  very  likely  that  it  is  also  formed  through  the  decomposition  of 
the  sodium  chlorid. 

Potassium  phosphate,  K2HP04,  is  found  in  association  with  sodium 
phosphate  in  all  the  fluids  and  solids.  As  it  has  similar  chemic  properties, 
its  functions  are  practically  the  same. 

Potassium  carbonate,  K2C03,  is  generally  found  with  the  preceding 
salt. 

MAGNESIUM  COMPOUNDS. 

Magnesium  phosphate,  Mg3(P04)2,  is  found  in  all  tissues,  in  associa- 
tion with  calcium  phosphate,  though  in  much  smaller  quantity. 

Magnesium  carbonate,  MgC03,  occurs  only  in  traces  in  the  blood. 
Both  of  these  compounds  have  functions  similar  to  the  calcium  com- 
pounds, and  exist,  in  all  probability,  under  similar  conditions. 


32  HUMAN   PHYSIOLOGY. 

IRON  COMPOUNDS. 

Iron  is  a  constituent  of  the  coloring  matter  of  the  blood.  Traces,  how- 
ever, are  also  found  in  lymph,  bile,  gastric  juice,  and  in  the  pigment  of  the 
eyes,  skin,  and  hair.  The  amount  of  iron  contained  in  a  body  weighing 
seventy-five  kilograms  is  about  three  gm.  It  exists  under  various  forms — 
e.  g.,  ferric  oxid,  ferrous  oxid,  and  in  combination  with  organic  com- 
pounds. 

Chemic  analysis  thus  shows  that  the  chemic  elements  into  which  the 
compounds  may  be  resolved  by  an  ultimate  analysis  do  not  exist  in  the  body 
in  a  free  state,  but  only  in  combination,  and  in  characteristic  proportions, 
to  form  compounds  whose  properties  are  the  resultant  of  those  of  the  ele- 
ments. Of  the  four  principal  elements  which  make  up  ninety-seven  per 
cent,  of  the  body,  O,  H,  N  are  extremely  mobile,  elastic,  and  possessed  of 
great  atomic  heat.  C,  H,  N  are  distinguished  for  the  narrow  range  of  their 
affinities,  and  for  their  chemic  inertia.  C  possesses  the  great  atomic  co- 
hesion.    O  is  noted  for  the  number  and  intensity  of  its  combinations. 

As  the  properties  of  the  compounds  formed  by  the  union  of  elements 
must  be  the  resultants  of  the  properties  of  the  elements  themselves,  it  fol- 
lows that  the  ternary  compounds,  starches,  sugars,  and  fats  must  possess 
more  or  less  inertia,  and  at  the  same  time  instability  ;  while  in  the  more 
complex  proteids,  in  which  sulphur  and  phosphorus  are  frequently  com- 
bined with  the  four  principal  elements,  molecular  instability  attains  its 
maximum.  As  all  the  foregoing  compounds  possess  in  varying  degrees  the 
properties  of  inertia  and  instability,  it  follows  that  living  matter  must 
possess  corresponding  properties,  and  the  capability  of  undergoing  un- 
ceasingly a  series  of  chemic  changes,  both  of  composition  and  decom- 
position, in  response  to  the  chemic  and  physical  influences  by  which  it  is 
surrounded,  and  which  underlie  all  the  phenomena  of  life. 

PRINCIPLES  OF  DISSIMILATION. 

In  addition  to  the  previously  mentioned  compounds, — viz.,  carbo- 
hydrates, fats,  proteids,  and  inorganic  salts, — there  is  obtained  by  chemic 
analysis  from  the  tissues  and  fluids  of  the  body  : 

1.  A  number  of  organic  acids,  such  as  acetic,  lactic,  oxalic,  butyric,  pro- 
pionic, etc.,  in  combination  with  alkaline  and  earthy  bases. 

2.  Organic  compounds,  such  as  alcohol,  glycerin,  cholesterin. 

3.  Pigments,  such  as  those  found  in  bile  and  urine. 

4.  Crystal lizable  nitrogenized  bodies,  such  as  urea,  uric  acid,  xanthin,  hip- 
puric  acid,  creatin,  creatinin,  etc. 


PHYSIOLOGY   OF  THE   CELL.  33 

While  some  few  of  these  compounds  may  possibly  be  regarded  as  neces- 
sary to  the  physiologic  integrity  of  the  tissues  and  fluids,  the  majority  of 
them  are  to  be  regarded  as  products  of  dissimilation  of  the  tissues  and 
foods  in  consequence  of  functional  activity,  and  represent  stages  in  their 
reduction  to  simpler  forms  previous  to  being  eliminated  from  the  body. 


PHYSIOLOGY    OF    THE    CELL. 

A  microscopic  analysis  of  the  tissues  shows  that  they  can  be  resolved 
into  simpler  elements,  termed  cells,  which  may,  therefore,  be  regarded  as 
the  primary  units  of  structure.  Though  cells  vary  considerably  in  shape, 
size,  and  chemic  composition  in  the  different  tissues  of  the  adult  body, 
they  are,  nevertheless,  descendants  from  typical  cells,  known  as  embryonic 
or  undifferentiated  cells,  examples  of  which  are  the  leukocytes  of  the  blood 
and  lymph  and  the  first  offspring  of  the  fertilized  ovum.  Ascending  the 
line  of  embryonic  development,  it  will  be  found  that  every  organized  body 
originates  in  a  single  cell — the  ovum.  As  the  cell  is  the  elementary  unit 
of  all  tissues,  the  function  of  each  tissue  must  be  referred  to  the  function 
of  the  cell.  Hence  the  cell  may  be  defined  as  the  primary  anatomic  and 
physiologic  unit  of  the  organic  world,  to  which  every  exhibition  of  life, 
whether  normal  or  abnormal,  is  to  be  referred. 

Structure  of  Cells. — Though  cells  vary  in  shape  and  size  and  internal 
structure  in  different  portions  of  the  body,  a  typical  cell  may  be  said  to 
consist  mainly  of  a  gelatinous  substance  forming  the  body  of  the  cell, 
termed  protoplasm  or  bioplasm,  in  which  is  embedded  a  smaller  spheric 
body,  the  nucleus.  The  shape  of  the  adult  cell  varies  according  to  the 
tissue  in  which  it  is  found  ;  when  young  and  free  to  move  in  a  fluid 
medium,  the  cell  assumes  a  spheric  form,  but  when  subjected  to  pressure, 
may  become  cylindric,  fusiform,  polygonal,  or  stellate.  Cells  vary  in  size 
within  wide  limits,  ranging  from  g^Vo  °f  an  mcn»  the  diameter  of  a  red 
blood- corpuscle,  to  ^jjo  °^  an  mcn>  the  diameter  of  the  large  cells  in  the 
gray  matter  of  the  spinal  cord.      (See  Fig.  2.) 

The  cell  protoplasm  consists  of  a  soft,  semifluid,  gelatinous  material, 
varying  somewhat  in  appearance  in  different  tissues.  Though  frequently 
homogeneous,  it  often  exhibits  a  finely  granular  appearance  under  medium 
powers  of  the  microscope.  Young  cells  consist  almost  entirely  of  clear 
protoplasm.  Mature  cells  contain,  according  to  the  tissue  in  which  they 
are  found,  material  of  an  entirely  different  character — e.  g.,  small  globules 
of  fat,  granules  of  glycogen,  mucigen,  pigments,  digestive  ferments,  etc. 


34 


HUMAN   PHYSIOLOGY. 


Under  high  powers  of  the  microscope  the  cell  protoplasm  is  found  to  be 
pervaded  by  a  network  of  fibers,  termed  spongioplasm,  in  the  meshes  of 
which  is  contained  a  clearer  and  more  fluent  substance,  the  hyaloplasm. 
The  relative  amount  of  these  two  constituents  varies  in  different  cells,  the 
proportion  of  hyaloplasm  being  usually  greater  in  young  cells.  The 
arrangement  of  the  fibers  forming  the  spongioplasm  also  varies,  the  fibers 
having  sometimes  a  radial  direction,  in  others  a  concentric  disposition,  but 
most  frequently  being  distributed  evenly  in  all  directions.  In  many  cells 
the  outer  portion  of  the  cell  protoplasm  undergoes  chemic  changes  and  is 
transformed  into  a  thin,  transparent,  homogeneous  membrane, — the  cell 
membrane, — which  completely  incloses  the  cell  substance.     The  cell  mem- 


Nuclear  mem- 
brane. 


Linin. 


Nuclear  fluid 
(matrix). 


Nucleolus. 


Chromatin 

cords  (nuclear 

network ) . 

Nodal  enlarge- 
ments of  the 
chromatin. 


Cell  membrane. 
Exoplasm. 

Microsomes. 
Centrosome 

Spongioplasm. 
Hyaloplasm. 


Foreign  inclo- 
sures. 


Fig.  2. — Diagram  of  a  Cell. 
Microsomes  and  spongioplasm  are  only  partly  drawn. 


brane  is  permeable  to  water  and  watery  solutions  of  various  inorganic  and 
organic  substances.     It  is,  however,  not  an  essential  part  of  the  cell. 

The  nucleus  is  a  small  vesicular  body  embedded  in  the  protoplasm  near 
the  center  of  the  cell.  In  the  resting  condition  of  the  cell  it  consists  of  a 
distinct  membrane,  composed  of  amphipyrenin^  inclosing  the  nuclear  con- 
tents. The  latter  consists  of  a  homogeneous  amorphous  substance, — the 
nuclear  matrix, — in  which  is  embedded  the  nuclear  network.  It  can  often 
be  seen  that  a  portion  of  one  side  of  the  nucleus,  called  the  pole,  is  free  from 


PHYSIOLOGY   OF  THE  CELL.  35 

this  network.  The  main  cords  of  the  network  are  arranged  as  V-shaped 
loops  about  it.  These  main  cords  send  out  secondary  branches  or  twigs, 
—which,  uniting  with  one  another,  complete  the  network.  The  nuclear 
cords  are  composed  of  granules  of  chromatin, — so  called  because  of  its 
affinity  for  certain  staining  materials, — held  together  by  an  achromatin  sub- 
stance known  as  linin.  Besides  the  nuclear  network,  there  are  embedded 
in  the  nuclear  matrix  one  or  more  small  bodies  composed  of  py renin , 
known  as  nucleoli.  At  the  pole  of  the  nucleus,  either  within  or  just 
without  in  the  protoplasm,  is  a  small  body,  the  centrosome,  or  pole  corpuscle. 
Chemic  Composition  of  the  Cell. — The  composition  of  living  pro- 
toplasm is  difficult  of  determination,  for  the  reason  that  all  chemic  and 
physical  methods  employed  for  its  analysis  destroy  its  vitality,  and  the  prod- 
ucts obtained  are  peculiar  to  dead  rather  than  to  living  matter.  Moreover, 
as  protoplasm  is  the  seat  of  constructive  and  destructive  processes,  it  is  not 
easy  to  determine  whether  the  products  of  analysis  are  crude  food  con- 
stituents or  cleavage  or  disintegration  products.  Nevertheless,  chemic  in- 
vestigations have  shown  that  even  in  the  living  condition  protoplasm  is  a 
highly  complex  compound — the  resultant  of  the  intimate  union  of  many 
different  substances.  About  seventy-five  per  cent,  of  protoplasm  consists 
of  water  and  twenty-five  per  cent,  of  solids,  of  which  the  more  important 
compounds  are  various  nucleo-proteids  (characterized  by  their  large  per- 
centage of  phosphorus),  globulins,  traces  of  lecithin,  cholesterin,  and  fre- 
quently fat  and  carbohydrates.  Inorganic  salts,  especially  the  potassium, 
sodium,  and  calcium  chlorids  and  phosphates,  are  almost  invariable  and 
essential  constituents. 

MANIFESTATIONS    OF    CELL   LIFE. 

Growth,  Nutrition. — All  cells  exhibit  the  three  fundamental  properties 
of  life — viz.,  growth,  nutrition,  reproduction.  All  cells  when  newly  repro- 
duced are  extremely  small,  but  by  the  absorption  of  nutritive  material  from 
their  surrounding  medium,  they  gradually  grow  until  they  attain  their 
mature  size.  This  is  accomplished  by  the  power  which  living  material  pos- 
sesses of  transforming,  vitalizing,  and  organizing  crude  nutritive  material, 
through  a  series  of  upward  changes,  into  material  similar  to  itself.  To  all 
these  changes  the  term  assimilation,  or  anabolism,  has  been  given.  Some 
of  the  absorbed  material,  in  all  probability,  never  becomes  an  integral  part 
of  the  living  bioplasm,  but  undergoes  disruption  and  oxidation,  giving  rise 
at  once  to  heat  and  force.  Coincident  with  the  assimilative  processes,  a 
series  of  disintegrative  processes  is  constantly  taking  place,  whereby  the 
living  material  is  reduced,  through  a  series  of  downward  chemic  changes,  to 


36  HUMAN   PHYSIOLOGY. 

simpler  compounds,  such  as  water,  carbon  dioxid,  urea,  etc.  To  all  these 
downward  changes  the  term  dissimilation,  or  katabolism,  has  been  given. 
As  a  result,  also,  of  these  various  changes,  the  protoplasm  gives  rise  to  the 
production  of  material  of  an  entirely  different  character,  such  as  globules 
of  fat,  granules  of  glycogen,  mucigen,  digestive  ferments,  etc.  The  sum 
total  of  all  changes  which  go  on  in  the  cell,  both  assimilative  and  dis- 
similative,  are  embraced  under  the  general  term  nutrition,  or  metabolism. 
Every  cell  presents  in  its  nutritive  activities  an  epitome  of  the  nutritive 
activities  of  the  body  as  a  whole. 

Physiologic  Properties  of  Protoplasm. — All  living  protoplasm  pos- 
sesses properties  which  serve  to  distinguish  and  characterize  it — viz.,  irrita- 
bility, conductivity,  and  motility. 

Irritability,  or  the  power  of  reacting  in  a  definite  manner  to  some  form 
of  external  excitation,  whether  mechanical,  chemic,  or  electric,  is  a  funda- 
mental property  of  all  living  protoplasm.  The  character  and  extent  of  the 
reaction  will  vary,  and  will  depend  both  on  the  nature  of  the  protoplasm  and 
the  character  and  strength  of  the  stimulus.  If  the  protoplasm  be  muscle, 
the  response  will  be  a  contraction  ;  if  it  be  gland,  the  response  will  be  secre- 
tion ;  if  it  be  nerve,  the  response  will  be  a  sensation  or  some  other  form  of 
nerve  activity. 

Conductivity,  or  the  power  of  transmitting  molecular  disturbances  aris- 
ing at  one  point  to  all  portions  of  the  irritable  material,  is  also  a  character- 
istic feature  of  all  protoplasm.  This  power,  however,  is  best  developed  in 
that  form  of  protoplasm  found  in  nerves,  which  serves  to  transmit,  with 
extreme  rapidity,  molecular  disturbances  arising  at  the  periphery  to  the 
brain,  as  well  as  in  the  reverse  direction.  Muscle  protoplasm  also  pos- 
sesses the  same  power  in  a  high  degree. 

Motility,  or  the  power  of  executing  apparently  spontaneous  movements, 
is  exhibited  by  many  forms  of  cell  protoplasm.  In  addition  to  the  molec- 
ular movements  which  take  place  in  certain  cells,  other  forms  of  movement 
are  exhibited,  more  or  less  constantly,  by  many  cells  in  the  animal  body — 
e.  g.,  the  waving  of  cilia,  the  ameboid  movements  and  migrations  of 
white  blood -corpuscles,  the  activities  of  spermatozooids,  the  projections  of 
pseudopodia,  etc.  These  movements,  arising  without  any  recognizable 
cause,  are  frequently  spoken  of  as  spontaneous.  Strictly  speaking,  how- 
ever, all  protoplasmic  movement  is  the  resultant  of  natural  causes,  the  true 
nature  of  which  is  beyond  the  reach  of  present  methods  of  investigation. 

Reproduction. — Cells  reproduce  themselves  in  the  higher  animals  in 
two  ways — by  direct  division  and  by  indirect  division,  or  karyokinesis.     In 


THYSIOLOGY    OF   THE   CELL. 


37 


the  former  the  nucleus  becomes  constricted,  and  divides  without  any  special 
grouping  of  the  nuclear  elements.  It  is  probable  that  this  occurs  only  in 
disintegrating  cells,  and  never  in  a  physiologic  multiplication.  In  divi- 
sion by  karyokinesis  (Fig.  3)  there  is  a  progressive  rearranging  and 
definite  grouping  of  the  nucleus,  the  result  of  which  changes  is  the  division 
of  the  centrosome,  the  chromatin,  and  the  rest  of  the  nucleus  into  two 
equal  portions,  which  form  the  nuclei.  Following  the  division  of  the  nuclei, 
the  protoplasm  divides.     The  process  may  be  divided  into  three  phases  : 


Close  Skein 
(viewed  from 
the  side). 
Polar  field. 


Loose  Skein  (viewed 

from  above — i.  e.,  from 

the  pole). 


Mother  Stars  (viewed  from  the  side). 


Mother  Star  (viewed         Daughter  Star.  Beginning.  Completed, 

from  above).  Division  of  the  Protoplasm. 

Fig.   3. — Karyokinetic  Figures  Observed    in  the  Epithelium  of  the    Oral 
Cavity  of  a  Salamander. 

The  picture  in  the  upper  right-hand  corner  is  from  a  section  through  a  dividing  egg  of 
Siredon  pisciformis.  Neither  the  centrosomes  nor  the  first  stages  of  the  develop- 
ment of  the  spindle  can  be  seen  by  this  magnification.     X  560- 


Prophase. — The  centrosoma,  at  first  small  and  lying  within  the  nucleus, 
increases  in  size  and  moves  into  the  protoplasm,  where  it  lies  near  the 
nucleus,  surrounded  by  a  clear  zone,  from  which  delicate  threads  radiate 
through  an  area  known  as  the  attraction  sphere.  The  nucleus  enlarges 
and  becomes  richer  in  chromatin.  The  lateral  twigs  of  the  chromatin 
cords  are  drawn  in,  while  the  main  cords  become  much  contorted.    These 


38  HUMAN  PHYSIOLOGY. 

cords  have  a  general  direction  transverse  to  the  long  axis  of  the  cell,  and 
parallel  to  the  plane  of  future  cleavage.  They  are  seen  as  V-shaped  seg- 
ments or  loops,  chromosomes,  having  their  closed  ends  directed  toward 
a  common  center,  the  polar  field,  while  the  other  ends  interdigitate  on  the 
opposite  side  of  the  nucleus — the  anti-pole.  The  polar  field  corre- 
sponds to  the  area  occupied  by  the  centrosoma.  This  arrangement  is 
known  as  the  close  skein  ;  but  as  the  process  goes  on,  the  chromosomes 
become  thicker,  shorter  and  less  contorted,  producing  a  much  looser 
arrangement,  known  as  the  loose  skein.  During  the  formation  of  the 
loose  skein,  the  centrosoma  divides  into  two  portions,  which  move  apart 
to  positions  at  the  opposite  ends  of  the  long  axis  of  the  nucleus.  At 
the  same  time  delicate  achromatin  fibers  make  their  appearance,  arranged 
in  the  form  of  a  double  cone,  the  apices  of  which  correspond  in  position 
to  the  centrosoma.  This  is  known  as  the  nuclear  spindle.  During  the 
prophase  the  nuclear  membrane  and  the  nucleoli  disappear. 

2.  The  Metaphase. — The  two  centrosomata  are  at  opposite  ends  of  the  long 
axis  of  the  nucleus,  each  surrounded  by  an  attraction  sphere,  now  called 
the  polar  radiation.  The  chromosomes  become  yet  shorter  and  thicker, 
and  move  toward  the  equator  of  the  nucleus,  where  they  lie  with  their 
closed  ends  toward  the  axis,  presenting  the  appearance,  when  seen  from 
the  poles,  of  a  star, — the  so-called  mother  star,  or  monaster.  While 
moving  toward  the  equator  of  the  nucleus,  and  often  earlier,  each 
chromosome  undergoes  longitudinal  cleavage,  the  sister  loops  remaining 
together  for  a  time.  Upon  the  completion  of  the  monaster,  one  loop  of 
each  pair  passes  to  each  pole  of  the  nucleus,  guided,  and  perhaps 
drawn  by  the  threads  of  the  nuclear  spindle.  The  separation  of  the 
sister  segments  begins  at  their  apices,  and  as  the  open  ends  are  drawn 
apart  they  remain  connected  by  delicate  achromatin  filaments  drawn  out 
from  the  chromosomes.  This  separation  of  the  daughter  chromosomes, 
and  their  movement  toward  the  daughter  centrosomata,  is  called  meta- 
kinesis.  As  they  approach  their  destination,  we  have  the  appearance  of 
two  stars  in  the  nucleus — the  daughter  stars,  or  diasters. 

3.  Anaphase. — The  daughter  stars  undergo,  in  reverse  order,  much  the 
same  changes  that  the  mother  star  passed  through.  The  chromosomes 
become  much  convoluted,  and  perhaps  united  to  one  another,  the  lateral 
twigs  appear,  and  the  chromatin  resumes  the  appearance  of  the  resting 
nucleus.  The  nuclear  spindle,  with  most  of  the  polar  radiation,  disap- 
pears, and  the  nucleoli  and  the  nuclear  membrane  reappear,  thus  forming 
two  complete  daughter  nuclei.  Meanwhile  the  protoplasm  becomes  con- 
stricted midway  between  the  young  nuclei.     This  constriction  gradually 


HISTOLOGY   OF   THE    EPITHELIAL   AND   CONNECTIVE   TISSUES.  39 

deepens  until  the  original  cell  is  divided,  with  the  formation  of  two  com- 
plete cells. 

HISTOLOGY    OF   THE    EPITHELIAL    AND 
CONNECTIVE    TISSUES. 

i.    EPITHELIAL  TISSUE. 

The  epithelial  tissue  consists  of  one  or  more  layers  of  cells  resting 
on  a  homogeneous  membrane,  the  other  side  of  which  is  abundantly  sup- 
plied with  blood-vessels  and  nerves.  The  form  of  the  epithelial  cell  varies 
in  different  situations,  and  may  be  flattened,  cuboid,  spheroid,  or  columnar. 
The  form  of  the  cell  in  all  instances  is  related  to  some  specific  function. 
When  arranged  in  layers  or  strata,  the  cells  are  cemented  together  by  an 
intercellular  substance — mucin. 

The  epithelial  tissue  forms  a  continuous  covering  for  the  surfaces  of  the 
body.  The  external  investment  (the  skin)  and  the  internal  investment  (the 
mucous  membrane,  which  lines  the  entire  alimentary  canal  and  its  associ- 
ated body  cavities)  are  both  formed,  in  all  situations,  by  the  homogeneous 
basement  membrane,  covered  with  one  or  more  layers  of  cells.  All  ma- 
terials, therefore,  whether  nutritive,  secretory,  or  excretory,  must  pass 
through  epithelial  cells  before  they  can  enter  into  the  formation  of  the 
tissues  or  be  eliminated  from  them.  The  nutrition  of  the  epithelial  tissue 
is  maintained  by  the  nutritive  material  derived  from  the  blood  diffusing 
itself  into  and  through  the  basement  membrane.  Chemically,  the  epithelial 
cells  of  the  epidermis — hair,  nails,  etc. — are  composed  of  an  albuminoid 
material  (keratin),  a  small  quantity  of  water,  and  inorganic  salts.  In  other 
situations,  especially  on  the  mucous  membranes,  the  cells  consist  largely  of 
mucin,  in  association  with  other  albuminoids.  The  consistency  of  epithe- 
lium varies  in  accordance  with  external  influences,  such  as  the  presence  or 
absence  of  moisture,  pressure,  friction,  etc.  This  is  well  seen  in  the  skin  of 
the  palms  of  the  hands  and  the  soles  of  the  feet — situations  where  it  acquires 
its  greatest  density.  In  the  alimentary  canal,  in  the  lungs,  and  in  other  cavi- 
ties, where  the  reverse  conditions  prevail,  the  epithelium  is  extremely  soft. 
Epithelial  tissues  also  possess  varying  degrees  of  cohesion  and  elasticity — 
physical  properties  which  enable  them  to  resist  considerable  pressure  and 
distention  without  having  their  physiologic  integrity  destroyed.  Inasmuch 
as  these  tissues  are  poor  conductors  of  heat,  they  assist  in  preventing  too 
rapid  radiation  of  heat  from  the  body,  and  cooperate  with  other  mechanisms 
in  maintaining  the  normal  temperature.  The  physiologic  activity  of  all 
epithelial  tissue  depends  on  a  due  supply  of  nutritive  material  derived  from 


40  HUMAN   PHYSIOLOGY. 

the  blood,  which  not  only  maintains  its  own  nutrition,  but  affords  those 
materials  out  of  which  are  formed  the  secretions  of  the  glands,  whether  of 
the  skin  or  mucous  membrane. 

Functions  of  Epithelial  Tissue. — In  succeeding  chapters  the  form, 
chemic  composition,  and  functions  of  epithelial  cells  will  be  considered  in 
connection  with  the  functions  of  the  organs  of  which  they  constitute  a  part. 
In  this  connection  it  may  be  stated  in  a  general  way  that  the  functions  of 
the  epithelial  tissues  are  : 

i .  To  serve  on  the  surface  of  the  body  as  a  protective  covering  to  the  under- 
lying structures  v  which  collectively  form  the  true  skin,  thus  protecting 
them  from  the  injurious  influences  of  moisture,  air,  dust,  microorgan- 
isms, etc. ,  which  would  otherwise  impair  their  vitality.  Wherever  con- 
tinuous pressure  is  applied  to  the  skin,  as  on  the  palms  of  the  hands  and 
soles  of  the  feet,  the  epithelium  increases  in  thickness  and  density,  and 
thus  prevents  undue  pressure  on  the  nerves  of  the  true  skin.  The  density 
of  the  epidermis  enables  it  to  resist,  within  limits,  the  injurious  influences 
of  acids,  alkalies,  and  poisons. 

2.  To  promote  absorption.  Inasmuch  as  the  skin  and  mucous  membranes 
cover  the  surfaces  of  the  body,  it  is  obvious  that  all  nutritive  material 
entering  the  body  must  first  traverse  the  epithelial  tissue.  Owing  to  their 
density,  however,  the  epithelial  cells  covering  the  skin  play  but  a  feeble 
role  as  absorbing  agents  in  man  and  the  higher  animals.  The  epithelium 
of  the  mucous  membrane  of  the  alimentary  canal,  particularly  that  of 
the  small  intestine,  is  especially  adapted,  from  its  situation,  consistency, 
and  properties,  to  play  the  chief  role  in  the  absorption  of  new  materials 
into  the  blood.  The  epithelium  lining  the  air-vesicles  of  the  lungs  is 
engaged  in  promoting  the  absorption  of  oxygen  and  the  exhalation  of 
carbon  dioxid. 

3.  To  form  secretions  and  excretions.  Each  secretory  gland  connected 
with  the  surfaces  of  the  body  is  lined  by  epithelial  cells,  which  are 
actively  concerned  in  the  formation  of  the  secretion  peculiar  to  the  gland. 
Each  excretory  organ  is  similarly  provided  with  epithelial  cells,  which 
are  engaged  either  in  the  production  of  the  constituents  of  the  excretion 
or  in  their  removal  from  the  blood. 

2.    THE  CONNECTIVE  TISSUES. 

The  connective  tissues,  in  their  collective  capacity,  constitute  a  frame- 
work which  pervades  the  body  in  all  directions,  and,  as  the  name  implies, 
serve  as  a  bond  of  connection  between  the  individual  parts,  at  the  same 


HISTOLOGY    OF   THE    EPITHELIAL    AND    CONNECTIVE   TISSUES.  41 

time  affording  a  basis  of  support  for  the  muscle,  nerve,  and  gland  tissues. 
The  connective-tissue  group  includes  a  number  of  varieties,  among  which 
may  be  mentioned  the  areolar,  adipose,  retiform,  white  fibrous,  yellow 
elastic,  cartilaginous  and  osseous.  Notwithstanding  their  apparent  diver- 
sity, they  possess  many  points  of  similarity.  They  have  a  common  origin, 
developing  from  the  same  embryonic  material ;  they  have  much  the  same 
structure,  passing  imperceptibly  into  one  another,  and  perform  practically 
the  same  functions. 

Areolar  Tissue. — This  variety  is  found  widely  distributed  throughout 
the  body.  It  serves  to  unite  the  skin  and  mucous  membrane  to  the  struc- 
tures on  which  they  rest ;  to  fomi  sheaths  for  the  support  of  blood-vessels, 
nerves,  and  lymphatics  ;  to  unite  into  compact  masses  the  muscular  tissue 
of  the  body,  etc.  Examined  with  the  naked  eye,  it  presents  the  appear- 
ance of  being  composed  of  bundles  of  fine  fibers  interlacing  in  every 
direction.  In  the  embryonic  state  the  elements  of  this  form  of  connective 
tissue  are  united  by  a  ground  substance,  gelatinous  in  character.  In  the 
adult  state  this  substance  shrinks  and  largely  disappears,  leaving  intercom- 
municating spaces  of  varying  size  and  shape,  from  which  the  tissue  takes 
its  name.  When  subjected  to  the  action  of  various  reagents,  and  examined 
microscopically,  the  bundles  can  be  shown  to  consist  of  extremely  delicate, 
colorless,  transparent,  wavy  fibers,  which  are  cemented  together  by  a  ground 
substance  composed  largely  of  mucin.  Other  fibers  are  also  observed, 
which  are  distinguished  by  a  straight  course,  a  sharp,  well-defined  outline, 
a  tendency  to  branch  and  unite  with  adjoining  fibers,  and  to  curl  up  at 
their  extremities  when  torn.  From  their  color  and  elasticity  they  are 
^known  as  yellow  elastic  fibers.  Distributed  throughout  the  meshes  of  the 
areolar  tissue  are  found  flattened,  irregularly  branched,  or  stellate  cor- 
puscles, connective- tissue  corpuscles,  plasma  cells,  and  granule  cells. 

Adipose  Tissue. — This  tissue,  which  exists  very  generally  throughout 
the  body,  though  found  most  abundantly  beneath  the  skin,  around  the  kid- 
neys, and  in  the  bones,  is  practically  but  a  modification  of  areolar  tissue. 
In  these  situations  it  presents  itself  in  small  masses  or  lobules  of  varying 
size  and  shape,  surrounded  and  penetrated  by  the  fibers  of  connective 
tissue.  Microscopic  examination  shows  that  these  masses  consist  of  small 
vesicles  or  cells,  round,  oval,  or  polyhedral  in  shape,  depending  somewhat 
on  pressure.  Each  vesicle  consists  of  a  thin,  colorless,  protoplasmic  mem- 
brane, thickened  at  one  point,  in  which  a  nucleus  can  usually  be  detected. 
This  membrane  incloses  a  globule  of  fat,  which  during  life  is  in  the  liquid 
state.  It  is  composed  of  olein,  stearin,  and  palmitin.  The  origin  of  the 
4 


42  HUMAN   PHYSIOLOGY. 

fat  is  to  be  referred  to  a  retrograde  change  in  the  protoplasmic  material  of 
the  connective-tissue  cells.  When  this  protoplasm  becomes  rich  in  carbon 
and  hydrogen,  it  is  speedily  converted  into  fat,  which  makes  its  appearance 
in  the  form  of  minute  drops  in  different  portions  of  the  cell.  As  the  drops 
accumulate,  at  the  expense  of  the  cell  protoplasm,  they  gradually  coalesce, 
until  there  remains  but  a  thin  stratum  of  the  protoplasm,  which  forms  the 
wall  of  the  vesicle.  Adipose  tissue  may,  therefore,  be  regarded  as  areolar 
tissue,  in  which,  and  at  the  expense  of  some  of  its  elements,  fat  is  stored  for 
the  future  needs  of  the  organism.  A  diminution  of  food,  especially  of 
fat  and  carbohydrates,  is  promptly  followed  by  an  absorption  of  fat  by  the 
blood-vessels  and  by  its  transference  to  the  tissues,  where  it  is  either  utilized 
for  tissue  construction  or  for  oxidation  purposes.  In  the  situations  in  which 
adipose  tissue  is  found  it  seems,  by  its  chemic  and  physical  properties,  to 
assist  in  the  prevention  of  a  too  rapid  radiation  of  heat  from  the  body,  to 
give  form  and  roundness,  and  to  diminish  angularities,  etc. 

Retiform  and  adenoid  tissue  are  also  modifications  of  areolar  tissue. 
The  meshes  of  the  former  contain  but  little  ground  substance,  its  place 
being  taken  by  fluids ;  the  meshes  of  the  latter  contain  large  numbers  of 
lymph  corpuscles. 

Fibrous  Tissue. — This  variety  of  connective  tissue  is  widely  distributed 
throughout  the  body.  It  constitutes  almost  entirely  the  ligaments  around 
the  joints,  the  tendons  of  the  muscles,  the  membranes  covering  organs  such 
as  the  heart,  liver,  nervous  system,  bones,  etc.  All  fibrous  tissue,  wherever 
found,  can  be  resolved  into  elementary  bundles,  which  on  microscopic 
examination  are  seen  to  consist  of  delicate,  wavy,  transparent,  homo- 
geneous fibers,  which  pursue  an  independent  course,  neither  branching  nor 
uniting  with  adjoining  fibers.  A  small  amount  of  ground  substance  serves 
to  hold  them  together.  Fibrous  tissue  is  tough  and  inextensible,  and  in 
consequence  is  admirably  adapted  to  fulfil  various  mechanical  functions  in 
the  body.  It  is,  however,  quite  pliant,  bending  easily  in  all  directions. 
When  boiled,  fibrous  tissue  yields  gelatin,  a  derivative  of  collagen. 

Elastic  Tissue. — The  fibers  of  elastic  tissue  are  usually  associated  in 
varying  proportions  with  the  white  fibrous  tissue  ;  but  in  some  structures — 
as  the  ligamentum  nuchoe,  the  ligamenta  subflava,  the  middle  coat  of  the 
larger  blood-vessels — the  elastic  fibers  are  almost  the  only  elements  present, 
and  give  to  these  structures  a  distinctly  yellow  appearance.  The  fibers 
throughout  their  course  give  off  many  branches,  which  unite  with  adjoin- 
ing branches  to  form  a  more  or  less  close  network.     As  the  name  implies, 


HISTOLOGY    OF   THE   EPITHELIAL   AND   CONNECTIVE  TISSUES.  43 

these  fibers  are  highly  elastic,  and  are  capable  of  being  extended  as  much 
as  sixty  per  cent,  before  breaking. 

Cartilaginous  Tissue. — This  form  of  connective  tissue  differs  from  the 
preceding  varieties  chiefly  in  its  density.  As  a  rule,  it  is  firm  in  consistency, 
though  somewhat  elastic.  It  is  opaque,  bluish-white  in  color,  though  in  thin 
sections  translucent.  All  cartilaginous  tissues  consist  of  connective-tissue  cells 
embedded  in  a  solid  ground  substance.  According  to  the  amount  and  tex- 
ture of  the  ground  substance,  three  principal  varieties  may  be  distinguished  : 

1 .  Hyaline  cartilage,  in  which  the  cells,  relatively  few  in  number,  are  em- 
bedded in  an  abundant  quantity  of  ground  substance.  The  body  of  the 
cells  is  in  many  instances  distinctly  marked  off  from  the  surrounding  sub- 
stance by  concentric  lines  or  fibers,  which  form  a  capsule  for  the  cell. 
Repeated  division  of  the  cell  substance  takes  place,  until  the  whole 
capsule  is  completely  occupied  by  daughter  cells.  The  ground  sub- 
stance is  pervaded  by  minute  channels,  which  communicate  on  one  hand 
with  the  spaces  around  the  cells,  and  on  the  other  with  lymph-spaces  in 
the  connective  tissue  surrounding  the  cartilage.  By  means  of  these  chan- 
nels, nutritive  fluid  can  permeate  the  entire  structure.  Hyaline  cartilage 
is  found  on  the  ends  of  the  long  bones,  where  it  enters  into  the  forma- 
tion of  the  joints  ;  between  the  ribs  and  sternum,  forming  the  costal 
cartilage,  as  well  as  in  the  nose  and  larynx. 

2.  White  fibro-cartilage,  the  ground  substance  of  which  is  pervaded  by 
white  fibers,  arranged  in  bundles  or  layers,  between  which  are  scattered 
the  usual  encapsulated  cells.  White  fibro-cartilage  is  tough,  resistant, 
but  flexible,  and  is  found  in  joints  where  strength  and  fixedness  are  re- 
quired. Hence  it  is  present  between  the  vertebrae,  forming  the  inter- 
vertebral discs,  between  the  condyle  of  the  lower  jaw  and  the  glenoid 
fossa,  in  the  knee-joint,  around  the  margins  of  the  joint  cavities,  etc.  In 
these  situations  it  assists  in  maintaining  the  apposition  of  the  bones,  in 
giving  a  certain  degree  of  mobility  to  the  joints,  and  in  diminishing  the 
effects  of  shock  and  pressure  imparted  to  the  bones. 

3.  Yellow  fibro-cartilage,  the  ground  substance  of  which  is  pervaded  by 
opaque,  yellow  elastic  fibers,  which  form,  by  the  interlacing  of  their 
branches,  a  complicated  network,  in  the  meshes  of  which  are  to  be  found 
the  usual  corpuscles.  '  As  these  fibers  are  elastic,  they  impart  to  the  car- 
tilage a  very  considerable  degree  of  elasticity.  Yellow  fibro-cartilage  is 
well  adapted,  therefore,  for  entering  into  the  formation  of  the  external 
ear,  epiglottis,  Eustachian  tube,  etc. — structures  which  require  for  their 
functional  activity  a  certain  degree  of  flexibility  and  elasticity. 


44  HUMAN   PHYSIOLOGY. 

Osseous  Tissue. — Osseous  tissue,  as  distinguished  from  bone,  is  a 
member  of  the  connective-tissue  group,  the  ground  substance  of  which  is 
permeated  with  insoluble  lime  salts,  of  which  the  phosphate  and  car- 
bonate are  the  most  abundant.  Immersed  in  dilute  solutions  of  hydro- 
chloric acid,  they  can  be  converted  into  soluble  salts  and  dissolved  out. 
The  osseous  matrix  left  behind  is  soft  and  pliable.  When  boiled,  it  yields 
gelatin. 

A  thin,  transverse  section  of  a  decalcified  bone,  when  examined  micro- 
scopically, reveals  a  number  of  small,  round  or  oval  openings,  which  repre- 
sent transverse  sections  of  canals  which  run  through  the  bone,  for  the 
most  part  in  a  longitudinal  direction,  though  frequently  anastomosing 
with  one  another.  These  so-called  Haversian  canals  in  the  living  state 
contain  blood-vessels  and  lymphatics. 

Around  each  Haversian  canal  is  a  series  of  concentric  laminae,  composed 
of  white  fibers.  Between  every  two  laminae  are  found  small  cavities 
(lacunae),  from  which  radiate  in  all  directions  small  canals  (canaliculi), 
which  communicate  freely  with  one  another.  The  Haversian  canals,  with 
their  associated  lacunae  and  canaliculi,  form  a  system  of  intercommuni- 
cating passages,  through  which  lymph  circulates  destined  for  the  nourish- 
ment of  bone.  Each  lacuna  contains  the  bone  corpuscle,  which  bears 
a  close  resemblance  to  the  usual  branched  connective-tissue  corpuscle,  and 
whose  function  appears  to  be  the  maintenance  of  the  nutrition  of  the 
bone. 

The  surface  of  every  bone  in  the  recent  state  is  invested  with  a  fibrous 
membrane,  the  periosteum,  except  where  it  is  covered  with  cartilage.  The 
inner  surface  of  this  membrane  is  loose  in  texture,  and  supports  a  fine 
plexus  of  capillary  blood-vessels  and  numerous  protoplasmic  cells — the 
osteoblasts.  As  this  layer  is  directly  concerned  in  the  formation  of  bone, 
it  is  spoken  of  as  the  osteogenetic  layer. 

A  section  of  a  bone  shows  that  it  is  composed  of  two  kinds  of  tissue — 
compact  and  cancellated.  The  compact  is  dense,  resembling  ivory,  and  is 
found  on  the  outer  portion  of  the  bone ;  the  cancellated  is  spongy,  and 
appears  to  be  made  up  of  thin,  bony  plates,  which  intersect  one  another  in  all 
directions,  and  is  found  in  greatest  abundance  in  the  interior  of  the  bones. 
The  shaft  of  a  long  bone  is  hollow.  This  central  cavity,  which  extends 
from  one  end  of  the  bone  to  the  other,  as  well  as  the  interstices  of  the  can- 
cellated tissue,  is  filled  in  the  living  state  with  marrow.  The  marrow  or 
medulla  is  composed  of  a  connective-tissue  framework  supporting  blood- 
vessels. In  its  meshes  are  to  be  found  characteristic  bone  cells  or  osteo- 
blasts, the  function  of  which  is  supposed  to  be  the  formation  of  bone.     In 


HISTOLOGY    OF   THE    EPITHELIAL   AND   CONNECTIVE   TISSUES.  45 

the  long  bones  the  marrow  is  yellow,  from  the  presence  in  the  connective- 
tissue  corpuscle  of  fat  globules,  which  arise  through  the  transformation  of 
the  cell  protoplasm.  In  the  cancellated  tissue,  near  the  extremities  of  the 
long  bones,  this  fatty  transformation  does  not  take  place  to  the  same  extent, 
and  the  marrow  appears  red.  The  cells  of  the  red  marrow  are  believed 
to  give  birth  indirectly  to  the  red  blood-corpuscles. 

Physical  and  Physiologic  Properties  of  Connective  Tissues. — 
Among  the  physical  properties  may  be  mentioned  consistency,  cohesion, 
and  elasticity.  Their  consistency  varies  from  the  semiliquid  to  the  solid 
state,  and  depends  on  the  quantity  of  water  which  enters  into  their  compo- 
sition. Their  cohesion,  except  in  the  softer  varieties,  is  very  considerable, 
and  offers  great  resistance  to  traction,  pressure,  torsion,  etc.  In  all  the 
movements  of  the  body,  in  the  contraction  of  muscles,  in  the  performance 
of  work,  the  consistence  and  cohesion  of  these  tissues  play  most  important 
roles.  Wherever  the  various  forms  of  connective  tissue  are  found,  their 
chemic  composition  and  structure  are  in  relation  to  their  functions.  If 
traction  be  the  preponderating  force,  the  structure  becomes  fibrous,  as  in 
ligaments  and  tendons,  and  the  cohesion  greatest  in  the  longitudinal  direc- 
tion. If  pressure  be  exerted  in  all  directions,  as  upon  membranes,  the 
fibers  interlace  and  offer  a  uniform  resistance.  When  pressure  is  exerted 
in  a  definite  direction,  as  on  the  extremities  of  the  long  bones,  the  tissue 
becomes  expanded  and  cancellated.  The  lamellae  of  the  cancellated  tissue 
arrange  themselves  in  curves  which  correspond  to  the  direction  of  the 
greatest  pressure  or  traction.  Extensibility  is  not  a  characteristic  feature, 
except  in  those  forms  containing  an  abundance  of  yellow  elastic  fibers. 
The  elasticity  is  an  essential  factor  in  many  physiologic  actions.  It  not 
only  opposes  and  limits  forces  of  traction,  pressure,  torsion,  etc.,  but  on 
their  cessation  returns  the  tissues  or  organs  to  their  original  condition. 
Elasticity  thus  assists  in  maintaining  the  natural  form  and  position  of  the 
organs  by  counterbalancing  and  opposing  temporarily  acting  forces. 

The  Skeleton. — The  connective  tissues  in  their  entirety  constitute  a 
framework  which  presents  itself  under  two  aspects  :  ( I )  As  a  solid,  bony 
skeleton,  situated  in  the  trunk  and  limbs,  affording  attachment  for  muscles 
and  viscera;  (2)  as  a  fine,  fibrous  skeleton,  found  everywhere  throughout 
the  body,  connecting  the  various  viscera  and  affording  support  for  the  epi- 
thelial, muscle,  and  nerve  tissues. 


46  HUMAN   PHYSIOLOGY. 


THE    PHYSIOLOGY    OF    THE    SKELETON. 

The  animal  body  is  characterized  by  the  power  of  executing  a  great 
variety  of  movements,  all  of  which  have  reference  to  a  change  of  relation 
of  one  part  of  the  body  to  another,  or  to  a  change  of  position  of  the  indi- 
vidual in  space,  as  in  the  various  acts  of  locomotion.  If  in  the  execution 
of  these  movements  the  different  parts  are  applied  or  directed  to  the  over- 
coming of  opposing  forces  in  the  environment,  the  animal  is  said  to  be  doing 
work.  In  the  conception  of  the  animal  body  as  a  machine  for  the  accom- 
plishment of  work  the  skeleton,  the  muscle  and  nerve  tissues  constitute  the 
three  primary  mechanisms,  all  of  which  bear  certain  definite  relations  one 
to  another. 

The  Skeleton  is  the  passive  framework,  the  axial  portion  of  which  (the 
vertebral  column,  head,  ribs,  and  sternum)  impart  more  or  less  fixity  and 
rigidity,  while  the  appendicular  portions  (the  bones  of  the  arms  and  legs) 
impart  extreme  mobility.  The  bones  of  the  arms  and  legs  more  especially 
may  be  looked  upon  as  constituting  a  system  of  levers,  the  fulcra  of  which, 
the  points  of  rest  around  which  they  move,  lie  in  the  joints. 

That  a  lever  may  be  effective  as  an  instrument  for  the  accomplishment  of 
work,  it  must  not  only  be  capable  of  moving  around  its  fulcrum,  but  it  must 
at  the  same  time  be  acted  on  by  two  opposing  forces,  one  passive,  the 
other  active.  In  the  movement  of  the  bony  levers  of  the  animal  body,  the 
passive  forces  are  largely  those  connected  with  the  environment,  e.  g., 
gravity,  cohesion,  friction,  elasticity,  etc.  The  active  forces  by  which  these 
latter  are  opposed  and  overcome  through  the  intermediation  of  the  bony 
levers  are  found  in  the  muscles  attached  to  them.  For  the  execution  of  all 
these  movements,  it  is  essential  that  the  relation  of  the  various  portions  of 
the  bony  skeleton  to  one  another  shall  be  such  as  to  permit  of  movement 
while  yet  retaining  close  apposition.  This  is  accomplished  by  the  mechan- 
ical conditions  which  have  been  evolved  at  the  points  of  union  of  bones, 
and  which  are  technically  known  as  articulations  or  joints. 

A  consideration  of  the  body  movements  involves  an  account  of  ( I )  the 
static  conditions,  or  those  states  of  equilibrium  in  which  the  body  is  at 
rest — e.  g.t  standing,  sitting ;  (2)  the  dynamic  conditions,  or  those  states  of 
activity  characterized  by  movement — e.g.,  walking,  running,  etc.  In  this 
connection,  however,  only  those  physical  and  physiologic  peculiarities  of 
the  skeleton,  especially  in  its  relation  to  joints,  will  be  referred  to 
which  underlie  and  determine  both  the  static  and  dynamic  states  of  the 
body. 


MECHANISM    OF   THE   SKELETON.  47 

Structure  of  Joints. — The  structures  entering  into  the  formation  of 
joints  are  : 

1.  Bones,  the  articulating  surfaces  of  which  are  often  more  or  less  ex- 
panded, especially  in  the  case  of  long  bones,  and  at  the  same  time  vari- 
ously modified  and  adapted  to  one  another  in  accordance  with  the  char- 
acter and  extent  of  the  movements  which  there  take  place. 

2.  Hyaline  cartilage,  which  is  closely  applied  to  the  articulating  end  of  each 
bone.  The  smoothness  of  this  form  of  cartilage  facilitates  the  move- 
ments of  the  opposing  surfaces,  while  its  elasticity  diminishes  the  force 
of  shocks  and  jars  imparted  to  the  bones  during  various  muscular  acts. 
In  a  number  of  joints,  plates  or  discs  of  white  fibro- cartilage  are  inserted 
between  the  surfaces  of  the  bones. 

3.  A  synovial  membrane,  which  is  attached  to  the  edge  of  the  hyaline 
cartilage,  entirely  inclosing  the  cavity  of  the  joint.  This  membrane  is 
composed  largely  of  connective  tissue,  the  inner  surface  of  which  is  lined 
by  endothelial  cells,  which  secrete  a  clear,  colorless,  viscid  fluid— the 
synovia.  This  fluid  not  only  fills  up  the  joint-cavity,  but,  flowing  over 
the  articulating  surfaces,  diminishes  or  prevents  friction. 

4.  Ligaments,  — tough,  inelastic  bands,  composed  of  white  fibrous  tissue,  — 
which  pass  from  bone  to  bone  in  various  directions  on  the  different  aspects 
of  the  joint.  As  white  fibrous  tissue  is  inextensible  but  pliant,  ligaments 
assist  in  keeping  the  bones  in  apposition,  and  prevent  displacement 
while  yet  permitting  of  free  and  easy  movements. 

Classification  of  Joints. — All  joints  may  be  divided,  according  to  the 

extent  and   kind  of  movements  permitted  by  them,  into  ( I )  diarthroses ; 

(2)  amphiarthroses  ;   (3)  synarthroses. 

I.  Diarthroses. — In  this  division  of  the  joints  are  included  all  those  which 
permit  of  free  movement.  In  the  majority  of  instances  the  articulating 
surfaces  are  mutually  adapted  to  each  other.  If  the  articulating  surface 
of  one  bone  is  convex,  the  opposing  but  corresponding  surface  is  con- 
cave. Each  surface,  therefore,  represents  a  section  of  a  sphere  or  a 
cylinder,  which  latter  arises  by  rotation  of  a  line  around  an  axis  in  space. 
According  to  the  number  of  axes  around  which  the  movements  take 
place  all  diarthrodial  joints  may  be  divided  into  : 

1.  Uniaxial  Joints. — In  this  group  the  convex  articulating  surface  is  a 
segment  of  a  cylinder  or  cone,  to  which  the  opposing  surface  more  or 
less  completely  corresponds.  In  such  a  joint  the  single  axis  of  rotation, 
though,  practically  is  not  exactly  at  right  angles  to  the  long  axis  of  the 
bone,  and  hence  the  movements — flexion  and  extension — which  take  place 
are  not  confined  to  one  plane.    Joints  of  this  character — e.  g.,  the  elbow, 


48  HUMAN    PHYSIOLOGY. 

knee,  ankle,  the  phalangeal  joints  of  the  fingers  and  toes — are,  therefore, 
termed  ginglymi,  or  hinge-joints.  Owing  to  the  obliquity  of  their  articu- 
lating surfaces,  the  elbow  and  ankle  are  cochleoid  or  screw-ginglymi. 
Inasmuch  as  the  axes  of  these  joints  on  the  opposite  sides  of  the  body 
are  not  coincident,  the  right  elbow  and  left  ankle  are  right-handed 
screws  ;  the  left  elbow  and  right  ankle,  left-handed  screws.  In  the 
knee-joint  the  form  and  arrangement  of  the  articulating  surfaces  are 
such  as  to  produce  that  modification  of  a  simple  hinge  known  as  a 
spiral  hinge,  or  helicoid.  As  the  articulating  surfaces  of  the  condyles  of 
the  femur  increase  in  convexity  from  before  backward,  and  as  the  inner 
condyle  is  longer  than  the  outer,  and,  therefore,  represents  a  spiral  sur- 
face, the  line  of  translation  or  the  movement  of  the  leg  is  also  a  spiral 
movement.  During  flexion  of  the  leg  there  is  a  simultaneous  inward 
rotation  around  a  vertical  axis  passing  through  the  outer  condyle  of  the 
femur ;  during  extension  a  reverse  movement  takes  place.  Moreover, 
the  slightly  concave  articulating  surfaces  of  the  tibia  do  not  revolve 
around  a  single  fixed  transverse  axis,  as  in  the  elbow-joint,  for  during 
flexion  they  slide  backward,  during  extension  forward,  around  a  shifting 
axis,  which  varies  in  position  with  the  point  of  contact. 

In  some  few  instances  the  long  axis  of  the  articulating  surface  is  par- 
allel rather  than  transverse  to  the  long  axis,  and  as  the  movement  then 
takes  place  around  a  more  or  less  conic  surface,  the  joint  is  termed  a 
trochoid  or  pulley — e.  g.y  the  odonto-atlantal  and  the  radio-ulnar.    In  the 
former  the  collar  formed  by  the  atlas  and  its  transverse  ligament  rotates 
around  the  vertical  odontoid  process  of  the  axis.      In  the  latter  the  head 
of  the  radius  revolves  around  its  own  long  axis  upon  the  ulna,  giving  rise 
to  the  movements  of  pronation  and  supination  of  the  hand.      The  axis 
around  which   these  two  movements  take   place  is  continued    through 
the  head  of  the  radius  to  the  styloid  process  of  the  ulna. 
2.   Biaxial  Joints. — In  this  group  the  articulating  surfaces  are  unequally 
curved,  though  intersecting  each  other.      When  the  surfaces  lie  in  the 
same  direction,  the  joint  is  termed  an  ovoid  joint — e.  g.,  the  radio-carpal 
and  the  atlanto-occipital.     As  the  axes  of  these  surfaces  are  vertical  to 
each  other,  the  movements  permitted  by  the  former  joint  are  flexion,  ex- 
tension, adduction,  and  abduction,  combined  with  a  slight  amount  of 
circumduction  ;  the  latter  joint  permits  of  flexion  and  extension  of  the 
head,  with  inclination  to  either  side.     When  the  surfaces  do  not  take 
the  same  direction,  the  joint,  from  its  resemblance  to  the  surfaces  of  a 
saddle,  is  termed  a  saddle-joint — e.  g.,   the  trapezio-metacarpal.     The 
movements  permitted  by  this  joint  are  also  flexion,  extension,  adduction, 
abduction,  and  circumduction. 


MECHANISM    OF   THE   SKELETON.  49 

3.  Polyaxial  Joints. — In  this  group  the  convex  articulating  surface  is  a 
segment  of  a  sphere,  which  is  received  by  a  socket  formed  by  the  oppos- 
ing articulating  surface.  In  such  a  joint,  termed  an  enarlhrodial  or 
ball-and-socket  joint, — e.  ^the  shoulder-joint,  hip-joint, — the  distal 
bone  revolves  around  an  indefinite  number  of  axes,  all  of  which  inter- 
sect one  another  at  the  center  of  rotation.  For  simplicity,  however,  the 
movement  may  be  described  as  taking  place  around  axes  in  the  three 
ordinal  planes — viz.,  a  transverse,  a  sagittal,  and  a  vertical  axis.  The 
movements  around  the  transverse  axis  are  termed  flexion  and  extension  ; 
around  the  sagittal  axis,  adduction  and  abduction  ;  around  the  vertical 
axis,  rotation.  When  the  bone  revolves  around  the  surface  of  an 
imaginary  cone,  the  apex  of  which  is  the  center  of  rotation  and  the  base 
the  curve  described  by  the  hand,  the  movement  is  termed  circumduc- 
tion. 

2.  Amphiarthroses. — In  this  division  are  included  all  those  joints  which 
permit  of  but  slight  movement — e.  g.,  the  intervertebral,  the  interpubic, 
and  the  sacro-iliac  joints.  The  surfaces  of  the  opposing  bones  are 
united  and  held  in  position  largely  by  the  intervention  of  a  firm,  elastic 
disc  of  fibro-cartilage.      Each  joint  is  also  strengthened  by  ligaments. 

3.  Synarthroses. — In  this  division  are  included  all  those  joints  in  which 
the  opposing  surfaces  of  the  bones  are  immovably  united,  and  hence  do 
not  permit  of  any  movement — e.  g.,  the  joints  between  the  bones  of  the 
skull. 

The  Vertebral  Column. — In  all  static  and  dynamic  states  of  the  body 
the  vertebral  column  plays  a  most  essential  role.  Situated  in  the  middle  of 
the  back  of  the  trunk,  it  forms  the  foundation  of  the  entire  skeleton.  It 
is  composed  of  a  series  of  superimposed  bones,  termed  vertebrae,  which 
increase  in  size  from  above  downward  as  far  as  the  brim  of  the  pelvic 
cavity.  Superiorly,  it  supports  the  skull  ;  laterally,  it  affords  attachment 
for  the  ribs,  which  in  turn  support  the  weight  of  the  upper  extremities ; 
below,  it  rests  upon  the  pelvic  bones,  which  transmit  the  weight  of  the  body 
to  the  inferior  extremities.  The  bodies  of  the  vertebrae  are  united  one  to 
another  by  tough  elastic  discs  of  fibro-cartilage,  which,  collectively,  con- 
stitute about  one  quarter  of  the  length  of  the  vertebral  column.  The  ver- 
tebrae are  held  together  by  ligaments  situated  on  the  anterior  and  posterior 
surfaces  of  their  bodies,  and  by  short,  elastic  ligaments  between  the  neural 
arches  and  processes.  These  structures  combine  to  render  the  vertebral 
column  elastic  and  flexible,  and  enable  it  to  resist  and  diminish  the  force 
of  shocks  communicated  to  it. 


50  HUMAN    PHYSIOLOGY. 

The  amphiarthrodial  character  of  the  intervertebral  joints  endows  the 
entire  column  with  certain  forms  of  movement  which  are  necessary  to 
the  performance  of  many  body  activities.  While  the  range  of  movement 
between  any  two  vertebrae  is  slight,  the  sum  total  of  movement  of  the  entire 
series  of  vertebrae  is  considerable.  In  different  regions  of  the  column  the 
character,  as  well  as  the  range  of  movement,  varies  in  accordance  with  the 
form  of  the  vertebrae  and  the  inclination  of  their  articular  processes.  In 
the  cervical  and  lumbar  regions  extension  and  flexion  are  freely  permitted, 
though  the  former  is  greater  in  the  cervical,  the  latter  in  the  lumbar  region, 
especially  between  the  fourth  and  fifth  vertebrae.  Lateral  flexion  takes 
place  in  all  portions  of  the  column,  but  is  particularly  marked  in  the  cer- 
vical region.  A  rotatory  movement  of  the  column  as  a  whole  takes  place 
through  an  angle  of  about  twenty-eight  degrees.  This  is  most  evident  in 
the  lower  cervical  and  dorsal  regions. 

The  skeleton  may,  therefore,  be  regarded  as  a  highly  developed  frame- 
work, which  determines  not  only  the  form  of  the  body,  and  affords  support 
and  protection  to  the  various  softer  organs  and  tissues,  but  also,  through  the 
mobility  of  its  joints,  permits  of  a  great  variety  of  complicated  movements. 


GENERAL    PHYSIOLOGY    OF    MUSCLE 
TISSUE. 

The  muscle  tissue,  which  closely  invests  the  bones  of  the  body,  and 
which  is  familiar  to  all  as  the  flesh  of  animals,  is  the  immediate  cause  of 
the  active  movements  of  the  body.  This  tissue  is  grouped  in  masses  of 
varying  size  and  shape,  which  are  technically  known  as  muscles..  The 
majority  of  the  muscles  of  the  body  are  connected  with  the  bones  of  the 
skeleton  in  such  a  manner  that,  by  an  alteration  in  their  form,  they  can 
change  not  only  the  position  of  the  bones  with  reference  to  one  another, 
but  can  also  change  the  individual's  relation  to  surrounding  objects.  They 
are,  therefore,  the  active  organs  of  both  motion  and  locomotion,  in  contra- 
distinction to  the  bones  and  joints,  which  are  but  passive  agents  in  the  per- 
formance of  ihe  corresponding  movements.  In  addition  to  the  muscle 
masses  which  are  attached  to  the  skeleton,  there  are  also  other  collections 
of  muscle  tissue  surrounding  cavities  such  as  the  stomach,  intestine,  blood- 
vessels, etc.,  which  impart  to  their  walls  motility,  and  so  influence  the 
passage  of  material  through  them. 

Muscles  produce  movement  of  the  structures  to  which  they  are  attached 
by  the  property  with  which   they  are  endowed  of  changing  their  shape, 


GENERAL   PHYSIOLOGY    OF   MUSCLE   TISSUE.  51 

shortening  or  contracting  under  the  influence  of  a  stimulus  transmitted  to 
them  from  the  nervous  system.     Muscles  are  therefore  divided  into  : 

1.  Voluntary  muscles,  comprising  those  whose  activity  is  called  forth  by 
stimuli  of  the  nerves  as  the  result  of  an  act  or  effort  of  volition. 

2.  Involuntary  muscles,  comprising  those  whose  activity  is  entirely  inde- 
pendent of  the  volition. 

The  voluntary  muscles  are  also  known  from  their  attachment  to  the 
skeleton  as  skeletal,  and  from  their  microscopic  appearance  as  striped 
muscles.  The  involuntary  muscles,  from  their  relation  to  the  viscera  of 
the  body,  are  known  also  as  visceral,  and  from  their  microscopic  appear- 
ance as  plain  or  smooth  muscles. 

General  Structure  of  Muscles. — All  skeletal  muscles  consist  of  a 
central  fleshy  portion,  the  body  or  belly,  which  is  provided  at  either  ex- 
tremity with  a  tendon  in  the  form  of  a  cord  or  membrane  by  which  it  is 
attached  to  the  bones.  The  body  is  the  contractile  region,  the  source  of 
activity ;  the  tendon  is  a  passive  region,  and  merely  transmits  the  activity 
to  the  bones. 

A  skeletal  muscle  is  a  complex  organ  consisting  of  muscular  fibers,  con- 
nective tissue,  blood-vessels,  and  lymphatics.  The  general  body  of  the 
muscle  is  surrounded  by  a  dense  layer  of  connective  tissue,  the  epimysium, 
which  blends  with  and  partly  forms  the  tendon ;  from  its  inner  surface 
septa  of  connective  tissue  pass  inward  and  group  the  muscle-fibers  into 
larger  and  smaller  bundles,  termed  fasciculi.  The  fasciculi,  invested  by 
this  special  sheath,  the  perimysium,  are  irregular  in  shape,  and  vary  con- 
siderably in  size.  The  fibers  of  the  fasciculi  are  separated  from  one  an- 
other and  supported  by  a  delicate  connective  tissue,  the  endomysium.  The 
connective  tissue  thus  surrounding  and  penetrating  the  muscle  binds  its 
fibers  into  a  distinct  organ,  and  affords  support  to  blood-vessels,  nerves, 
and  lymphatics.  The  muscle-fibers  are  arranged  parallel  to  one  another, 
and  their  direction  is  that  of  the  long  axis  of  the  muscle.  In  length  they 
vary  from  thirty  to  forty  millimeters,  and  in  diameter  from  twenty  to  thirty 
micromillimeters. 

The  vascular  supply  to  the  muscles  is  very  great,  and  the  disposition 
of  the  capillary  vessels,  with  reference  to  muscle-fiber,  is  very  charac- 
teristic. The  arterial  vessels,  after  entering  the  muscle,  are  supported  by 
the  perimysium  ;  in  this  situation  they  give  off  short,  transverse  branches, 
which  immediately  break  up  into  a  capillary  network  of  rectangular  shape, 
within  which  the  muscle-fibers  are  contained.  The  muscle-fiber  in  inti- 
mate relation  with  the  capillary  is  bathed  with  lymph  derived  from  it.     Its 


52  HUMAN    PHYSIOLOGY. 

contractile  substance,  however,  is  separated  from  the  lymph  by  its  own 
investing  membrane,  through  which  all  interchange  of  nutritive  and  waste 
materials  must  take  place.  Lymphatics  are  present  in  muscle,  but  are  con- 
fined to  the  connective  tissue,  in  the  spaces  of  which  they  have  their  origin. 
The  nerves  which  carry  the  stimuli  to  a  muscle  enter  near  its  geomet- 
ric center.  Many  of  the  fibers  pass  directly  to  the  muscle-fibers  with 
which  they  are  connected  ;  others  are  distributed  to  blood-vessels.  Every 
muscle-fiber  is  supplied  with  a  special  nerve-fiber,  except  in  those  instances 
where  the  nerve  trunks  entering  a  muscle  do  not  contain  so  many  fibers  as 
the  muscle.  In  such  cases  the  nerve-fibers  divide,  until  the  number  of 
branches  equals  the  number  of  muscle-fibers.  The  individual  muscle- 
fiber  is  penetrated  near  its  center  by  the  nerve,  the  ends  being  practically 
free  from  nerve  influence.  The  stimulus  that  comes  to  the  muscle-fiber 
acts  primarily  upon  its  center,  and  then  travels  in  both  directions  to  the  ends. 

Histology  of  the  Skeletal  Muscle-fiber. — A  muscle-fiber  consists  of  a 
transparent  elastic  membrane,  the  sarcolemma,  in  which  is  contained  the 
true  muscle  element.  Examined  microscopically,  the  fiber  presents  a  series 
of  alternate  dim  and  bright  bands,  giving  to  it  a  striated  appearance. 

When  the  bright  band  is  examined  with  high  magnifying  powers,  a  fine, 
dark  line  is  seen  crossing  it  transversely.  It  was  supposed  by  Krause  to 
be  the  optic  expression  of  a  membrane  which  divides  the  cavity  of  the 
sarcolemma  into  a  series  of  compartments,  each  of  which  contains  a  dim 
band  of  sarcous  or  muscle  substance,  bounded  at  either  extremity  with  the 
half  of  a  bright  band.  This  membrane  has  since  been  resolved  into  a  row 
of  granules. 

The  muscle-fiber  also  exhibits  a  longitudinal  striation,  indicating  that  it 
is  composed  of  fibrillae,  placed  side  by  side  and  embedded  in  some  inter- 
fibrillar  substance,  to  which  the  name  sarcoplasm  has  been  given.  The 
fibrillae,  which  are  arranged  longitudinally  to  the  long  axis  of  the  fiber,  are 
grouped  by  the  intervening  material  into  bundles  of  varying  size,  the 
muscle  columns.  The  fibrillse  which  extend  throughout  the  length  of  the 
fiber  are  not  of  uniform  thickness,  but  present  at  regular  intervals  well- 
marked  constrictions. 

In  the  region  of  the  dim  band  the  fibrilla  presents  itself  in  the  form  of 
a  homogeneous  prismatic  rod,  termed  sarcostyle,  separated  from  neighbor- 
ing rods  by  a  slight  amount  of  sarcoplasm.  Between  two  successive  rods 
is  found  a  dark  granule,  united  by  a  thin  band  of  similar  ma  erial  to  the 
ends  of  the  rods.  The  transverse  row  of  granules  corresponds  to  Krause' s 
membrane. 


GENERAL   PHYSIOLOGY    OF  MUSCLE   TISSUE.  53 

In  the  region  of  the  granules  there  is  a  diminution  of  the  sarcous  sub- 
stance, but  an  increase  in  the  amount  of  sarcoplasm,  and  as  the  latter  is 
more  transparent  than  the  former,  the  fiber  presents  at  this  point  a  con- 
spicuous bright  band.  Rollet  considers  the  sarcostyles  to  be  preexistent, 
not  the  result  of  post-mortem  or  chemic  changes,  and  the  seat  of  the  con- 
tractile elements.  The  sarcoplasm  is  a  passive  material  similar  in  its 
properties  to  protoplasm. 

Briicke  has  shown  that  when  the  muscle-fiber  is  examined  under 
crossed  Nichol  prisms  the  dim  band  appears  bright  and  the  bright  band 
appears  dim  against  a  dark  background,  indicating  that  the  former  is 
doubly  refractile,  or  anisotropic,  the  latter  singly  refractile,  or  isotropic. 
The  fiber,  therefore,  appears  to  be  composed  of  alternate  discs  of  aniso- 
tropic and  isotropic  substance. 

Structure  of  Non-striated  Muscle-fiber.  — As  the  name  implies, 
the  involuntary  fiber  is  non-striated,  being  apparently  uniform  and  homo- 
geneous in  appearance.  When  isolated,  the  fiber  presents  itself  in  the 
form  of  an  elongated  fusiform  cell,  varying  from  y1^  to  g^  of  an  inch 
in  length.  In  some  animals  the  fiber  exhibits  a  longitudinal  striation, 
as  if  it  were  composed  of  fibers.  The  cell  is  surrounded  by  a  thin, 
elastic  membrane,  and  contains  a  distinct  oval  nucleus.  The  fibers  are 
usually  arranged  in  bundles  and  lamellae,  and  held  together  by  a  cement 
substance  and  connective  tissue.  This  non-striated  muscle  tissue  is  found 
in  the  muscularis  mucosse  of  the  alimentary  canal  as  well  as  in  the 
muscular  walls  of  the  stomach  and  intestines,  in  the  posterior  part  of  the 
trachea,  in  the  bronchial  tubes,  in  the  walls  of  the  blood-vessels,  and  in 
many  other  situations. 

Chemic  Composition  of  Muscle. — The  chemic  composition  of  muscle 
is  imperfectly  understood,  owing  to  the  fact  that  some  of  its  constituents 
undergo  a  spontaneous  coagulation  after  death,  and  that  the  chemic 
methods  employed  also  tend  to  alter  its  normal  composition.  When  fresh 
muscle  is  freed  from  fat  and  connective  tissue,  frozen,  rubbed  up  in  a  mor- 
.tar,  and  expressed  through  linen,  a  slightly  yellow,  syrupy,  alkaline,  or 
neutral  fluid  is  obtained,  known  as  mtiscle  plasjna.  This  fluid  at  normal 
temperature  coagulates  spontaneously,  and  resembles  in  many  respects  the 
coagulation  of  blood  plasma.  The  coagulum  subsequently  contracts  and 
squeezes  out  an  acid  muscle  serum.  The  coagulated  mass  is  termed  myosin. 
This  proteid  belongs  to  the  class  of  globulins.  Inasmuch  as  it  is  not 
present  in  living  muscle,  and  makes  its  appearance  only  in  the  as  yet  living 
muscle  plasma,  it  is  probable  that  it  is  derived  from  some  preexisting  sub- 


54  HUMAN   PHYSIOLOGY. 

stance,  which  is  supposed  to  be  myosinogen.  Myosin  is  digested  by  pepsin 
and  trypsin.  According  to  Halliburton,  muscle  plasma  contains  the  follow- 
ing proteid  bodies :  Myosinogen,  paramyosinogen,  albumin,  myoalbumose, 
all  of  which  differ  in  chemic  composition  and  respond  to  various  chemic 
and  physical  reagents. 

Ferment  bodies,  such  as  pepsin  and  diastase ;  non-nitrogenized  bodies, 
such  as  glycogen,  lactic  and  sarcolactic  acids,  fatty  bodies,  and  inosite  ; 
nitrogenized  extractives — e.  g. ,  urea,  uric  acid,  kreatinin,  as  well  as  inor- 
ganic salts,  have  been  obtained  from  the  muscle  serum. 

Metabolism  in  Muscles. — The  chemic  changes  which  underlie  the 
transformation  of  energy  in  living  muscles  are  very  active  and  complex. 

As  shown  by  an  analysis  of  the  blood  flowing  to  and  from  the  resting 
muscle,  it  has,  while  passing  through  the  capillaries,  lost  oxygen  and 
gained  carbon  dioxid.  The  amount  of  oxygen  absorbed  by  the  muscle 
(nine  per  cent. )  is  greater  than  the  amount  of  C02  given  off  (6.7  per  cent. ). 
There  is  no  parallelism  between  these  two  processes,  as  C02  will  be  given 
off  in  the  absence  of  oxygen,  or  in  an  atmosphere  of  nitrogen. 

In  the  active  or  contracting  muscle  both  the  absorption  of  oxygen  and 
the  production  of  C02  are  largely  increased,  but  the  ratio  existing  between 
them  differs  considerably  from  that  of  the  resting  muscle,  for  the  quantity 
of  oxygen  absorbed  amounts  to  1 1. 26  per  cent.,  the  quantity  of  C02  to  10.8 
per  cent.  (Ludwig).  Moreover,  in  a  tetanized  muscle  the  quantity  of  CO., 
given  off  may  be  largely  in  excess  of  the  oxygen  absorbed.  From  these 
facts  it  is  evident  that  the  energy  of  the  contraction  does  not  depend  upon 
the  direct  oxidation  of  certain  substances,  but  upon  the  decomposition  of 
some  unstable  compound  of  high  potential  energy,  rich  in  carbon  and 
oxygen.  When  the  muscle  is  active,  its  tissue  changes  from  a  neutral  to  an 
acid  reaction,  from  the  development  of  sarcolactic  and  possibly  phosphoric 
acids.  The  amount  of  glycogen  present  in  muscle  (0.43  per  cent.) 
diminishes,  but  muscles  wanting  in  glycogen,  nevertheless,  retain  their 
power  of  contraction.  Water  is  absorbed.  The  amount  of  urea  is  not 
materially  increased  by  muscular  activity,  unless  it  is  excessive  and  pro- 
longed, and  then  only  in  the  absence  of  a  sufficient  quantity  of  non- 
nitrogenized  material.  Coincident  with  muscle  contraction,  the  blood- 
vessels become  widely  dilated,  leading  to  a  large  increase  in  the  blood-supply 
and  a  rapid  removal  of  products  of  decomposition. 

Rigor  Mortis. — A  short  time  after  death  the  muscles  pass  into  a  con- 
dition of  extreme  rigidity  or  contraction,  which  lasts  from  one  to  five  days. 
In  this  state   they  offer  great  resistance  to  extension,  their  tonicity  disap- 


GENERAL   PHYSIOLOGY   OF   MUSCLE   TISSUE.  55 

pears,  their  cohesion  diminishes,  their  irritability  ceases.  The  time  of  the 
appearance  of  this  post-mortem  or  cadaveric  rigidity  varies  from  a  quarter 
of  an  hour  to  seven  hours.  Its  onset  and  duration  are  influenced  by  the 
condition  of  the  muscular  irritability  at  the  time  of  death.  When  the 
irritability  is  impaired  from  any  cause,  such  as  disease  or  defective  blood- 
supply,  the  rigidity  appears  promptly,  but  is  of  short  duration.  After  death 
from  acute  diseases,  it  is  apt  to  be  delayed,  but  to  continue  for  a  longer  period. 

The  rigidity  appears  first  in  the  muscles  of  the  lower  jaw  and  neck  ;  next 
in  the  muscles  of  the  abdomen  and  upper  extremities  ;  finally  in  the  trunk 
and  lower  extremities.     It  disappears  in  practically  the  same  order. 

Chemic  changes  of  a  marked  character  accompany  this  rigidity.  The 
muscle  becomes  acid  in  reaction  from  the  development  of  sarcolactic  acid  ; 
it  gives  off  a  large  quantity  of  carbonic  acid,  and  is  shortened  and  dimin- 
ished in  volume. 

The  immediate  cause  of  the  rigidity  appears  to  be  a  coagulation  of  the 
myosinogen  within  the  sarcolemma,  with  the  subsequent  formation  of 
myosin  and  muscle  serum.  In  the  early  stages  of  coagulation  restitution  is 
possible  by  the  circulation  of  arterial  blood  through  the  vessels.  The  final 
disappearance  of  this  contraction  is  due  to  the  action  of  acids  dissolving 
the  myosin,  and  possibly  to  putrefactive  changes. 

Source  of  Muscular  Energy. — According  to  most  experimenters,  it 
is  certain  that  normal  muscle  activity  is  not  dependent  on  the  metabolism 
of  nitrogenous  materials,  inasmuch  as  its  chief  end  product,  urea,  is  not 
increased.  The  marked  production  of  C02  points  to  the  combustion  of 
some  non -nitrogenous  matter, — e.  g.,  glycogen, — especially  as  this  substance 
disappears  during  muscular  activity.  Muscles  wanting  in  glycogen  are, 
nevertheless,  capable  of  contracting  for  some  time.  Moreover,  there  is  no 
proof  of  the  direct  combustion  of  glycogen  or  any  other  carbohydrate.  It 
has  been  suggested  by  Hermann  that  the  energy  of  a  muscular  contraction 
may  be  due  to  the  splitting  and  subsequent  re-formation  of  a  complex  body 
belonging  neither  to  the  carbohydrates  nor  to  the  fats,  but  to  the  albumins. 
To  this  body  the  term  inogen  has  been  applied.  This  complex  molecule, 
the  product  of  the  metabolic  activity  of  the  muscle  cell,  in  undergoing  de- 
composition would  yield  C02,  sarcolactic  acid,  and  a  proteid  residue  resem- 
bling myosin.  With  the  cessation  of  the  contraction,  the  muscle  protoplasm 
recombines  the  proteid  residue  with  oxygen,  carbohydrates,  and  fats,  and 
again  forms  inogen. 

The  phenomena  of  rigor  mortis  support  such  a  view.  At  the  moment 
of  this  contraction  the  muscle  gives  off  C02  in  large  amqunts,  the  muscle 
becomes    acid,  and   myosin   is  formed,     There   is   thus  a  close    analogy 


56  HUMAN    PHYSIOLOGY. 

between  the  two  processes ;  in  other  words,  a  contraction  is  a  partial  death 
of  the  muscle.  As  to  what  becomes  of  the  myosin  formed  during  a  contrac- 
tion, nothing  is  known.     It  may  be  used  in  the  formation  of  new  inogen. 

The  Physical  Properties  of  Muscle  Tissue. — The  consistency  c' 
muscle  tissue  varies  considerably,  according  to  the  different  states  of  the 
muscle.  In  a  state  of  tension  it  is  hard  and  resistant ;  when  free  from 
tension,  it  is  soft  and  fluctuating,  whether  the  muscle  is  contracting  or  rest- 
ing. Tension  alone  produces  hardness.  The  cohesion  of  muscle  tissue 
is  less  than  that  of  connective  tissue,  and  is  broken  more  readily.  Cohesion 
resists  traction  and  pressure,  and  lasts  as  long  as  irritability  remains. 

The  elasticity  of  a  muscle,  though  not  great  is  almost  perfect.  After 
being  extended  by  a  weight,  it  returns  to  its  natural  form.  The  limit  of 
elasticity,  however,  is  soon  passed.  A  weight  of  50  or  100  grams  will 
overcome  the  elasticity  so  that  it  will  not  return  to  its  natural  length.  In 
inorganic  bodies  the  extension  is  directly  proportional  to  the  extending 
weight,  and  the  line  of  extension  is  straight.  With  muscles,  the  extension 
is  not  proportional  to  the  weight.  While  at  first  it  is  marked,  the  elonga- 
tion diminishes  as  the  weight  increases  by  equal  increments,  so  that  the 
line  of  extension  becomes  a  curve.  In  other  words,  the  elasticity  of  a 
passive  muscle  augments  with  increased  extension.  On  the  contrary,  the 
elasticity  of  an  active  is  less  than  that  of  a  passive  muscle,  for  it  is  elongated 
more  by  the  same  weight,  as  shown  by  experiment. 

Tonicity  is  a  property  of  all  muscles  in  the  body,  in  consequence  of 
being  normally  stretched  to  a  slight  extent  beyond  their  natural  length. 
This  may  be  due  to  the  action  of  antagonistic  muscles,  or  to  the  elasticity 
of  the  parts  of  the  skeleton  to  which  they  are  attached.  This  is  shown  by 
the  shortening  of  the  muscle  which  takes  place  when  it  is  divided.  Mus- 
cular tonus  plays  an  important  role  in  muscular  contraction.  Being  always 
on  the  stretch,  the  muscle  loses  no  time  in  acquiring  that  degree  of  tension 
necessary  to  its  immediate  action  on  the  bones.  Again,  the  working  power 
of  a  muscle  is  increased  by  the  presence  of  some  resistance  to  the  act  of 
contraction.  According  to  Marey,  the  amount  of  work  is  considerably 
increased  when  the  muscular  energy  is  transmitted  by  an  elastic  body  to 
the  mass  to  be  moved,  while  at  the  same  time,  the  shock  of  the  contraction 
is  lessened.  The  position  of  a  passive  limb  is  the  resultant  also  of  the 
elastic  tension  of  antagonistic  groups  of  muscles. 

Muscle  excitability  or  contractility  are  terms  employed  to  denote 
that  property  of  muscle  tissue  in  virtue  of  which  it  contracts  or  shortens 
in  response  to  various  excitants  or  stimuli.     Though  usually  associated  with 


GENERAL   PHYSIOLOGY   OF   MUSCLE  TISSUE.  57 

the  activity  of  the  nervous  system,  it  is,  nevertheless,  an  independent  en- 
dowment, and  persists  after  all  nervous  connections  are  destroyed.  If  the 
nerve  terminals  be  destroyed,  as  they  can  be  by  the  introduction  of  curara 
into  the  system,  the  muscles  become  completely  relaxed  and  quiescent. 
The  strongest  stimuli  applied  to  the  nerves  fail  to  produce  a  contraction. 
Various  external  stimuli  applied  directly  to  the  muscle  substance  produce 
at  once  the  characteristic  contraction.  The  excitability  of  muscle  is  there- 
fore an  inherent  property,  dependent  on  its  nutrition,  and  persisting  as  long 
as  it  is  supplied  with  proper  nutritive  materials  and  surrounded  by  those 
external  conditions  which  maintain  its  chemic  or  physical  integrity. 

Muscle  Contractions. — All  muscle  contractions  occurring  in  the  body 
under  normal  physiologic  conditions  are  either  voluntary,  caused  by  a 
volitional  effort  and  the  transmission  of  a  nerve  impulse  from  the  brain 
through  the  spinal  cord  and  nerves  to  the  muscles,  or  reflex,  caused  by 
a  peripheral  stimulation  and  the  transmission  of  a  nerve  impulse  to  the 
spinal  cord,  to  be  reflected  outward  through  the  same  nerves  to  the  muscles. 
In  either  case  the  resulting  contraction  is  essentially  the  same.  The  normal 
or  physiologic  sti7nulus  which  provokes  the  muscular  contraction  is  a 
nerve  impulse  the  nature  of  which  is  unknown,  but  is  perhaps  allied  to  a 
molecular  disturbance.  After  removal  from  the  body,  muscles  remain 
in  a  state  of  rest,  inasmuch  as  they  possess  no  spontaneity  of  action. 
Though  consisting  of  a  highly  irritable  tissue,  they  can  not  pass  from 
the  passive  to  the  active  state  except  upon  the  application  of  some  form  of 
stimulation. 

The  stimuli  which  are  capable  of  calling  forth  a  contraction  may  be 
divided  into — 

1.  Mechaniqal. 

2.  Chemic. 

3.  Physical. 

4.  Electric. 

Every  mechanical  stimulus  of  a  muscle, — e.  g.,  pick,  cut,  or  tap, — provid- 
ing it  has  sufficient  intensity,  and  is  repeated  with  sufficient  rapidity,  will 
cause  not  only  a  single  contraction,  but  a  series  of  contractions. 

All  chemic  agents  which  impair  the  chemic  composition  of  the  muscle 
with  sufficient  rapidity — e.  g.,  hydrochloric  acid,  acetic  and  oxalic  acids,  dis- 
tilled water  injected  into  the  vessels,  etc. — act  as  stimuli,  and  produce 
single  and  multiple  contractions.  Physical  agents,  as  heat  and  electricity, 
also  act  as  stimuli.  A  muscle  heated  rapidly  to  300  C.  contracts  vig- 
orously, and  reaches  its  maximum  at  450  C.  Of  all  forms  of  stimuli,  the 
5 


58  HUMAN   PHYSIOLOGY. 

electric  is  the  most  generally  used.     Two  forms  are  used — the  induced 
current  and  the  make-and-break  of  a  constant  current. 

Changes  in  a  Muscle  During  Contraction. — When  a  muscle  is 
stimulated,  either  indirectly  through  the  nerve  or  directly  by  any  external 
agent,  it  undergoes  a  series  of  changes,  which  relate  to  its  form,  volume, 
optic,  physical,  chemic,  and  electric  properties.  These  changes,  in  their 
totality,  constitute  the  muscular  contraction. 

i.  Form. — The  most  obvious  change  is  that  of  form.  The  fibers  become 
shorter  in  their  longitudinal  and  wider  in  their  transverse  diameters,  and 
the  muscle  as  a  whole  becomes  shorter  and  thicker.  The  degree  of 
shortening  may  amount  to  thirty  per  cent,  of  the  original  length. 

2.  Volume. — The  increase  in  transverse  diameter  does  not  fully  compen- 
sate for  the  diminution  in  length,  for  there  is  at  the  moment  of  contrac- 
tion a  slight  shrinkage  in  volume,  which  has  been  attributed  to  a  com- 
pression of  air  in  its  interstices. 

3.  Optic  Changes. — If  a  muscle-fiber  be  examined  microscopically  during 
its  contraction,  it  will  be  observed  that  when  the  contraction  wave 
begins,  both  bright  and  dim  bands  diminish  in  height  and  become 
broader,  though  this  change  is  more  noticeable  in  the  region  of  the  bright 
band.  This  Englemann  attributes  to  a  passage  of  fluid  material  from 
the  bright  into  the  dim  band.  At  the  time  of  relaxation  there  is  a  return 
of  this  material,  and  the  fiber  assumes  its  original  shape  and  volume. 
As  the  contraction  wave  reaches  its  maximum,  the  optic  properties  of 
both  the  isotropic  and  anisotropic  bands  change.  The  former,  which 
was  originally  clear,  now  becomes  darker  and  less  transparent,  until  at 
the  crest  of  the  wave  it  assumes  the  appearance  of  a  distinct  dark  band. 
The  latter,  the  anisotropic,  which  was  originally  dim,jiow  becomes,  in 
comparison,  clear  and  light.  This  change  in  optic  appearance  is  due 
to  an  increase  in  refrangibility  of  the  isotropic  and  a  decrease  in  the 
anisotropic  bands  coincident  with  the  passage  of  fluid  from  the  former 
into  the  latter.  There  is  at  the  height  of  the  contraction  a  complete 
reversal  in  the  positions  of  the  striations.  At  a  certain  stage  between  the 
beginning  and  the  crest  of  the  wave  there  is  an  intermediate  point,  at 
which  the  strix  almost  entirely  disappear,  giving  to  the  fiber  an  appear- 
ance of  homogeneity.  There  is,  however,  no  change  in  refractive  power, 
as  shown  by  the  polarizing  apparatus.  After  the  contraction  wave  has 
reached  the  stage  of  greatest  intensity,  there  is  a  reversal  of  the  foregoing 
phenomena,  and  the  fiber  returns  to  its  original  condition,  which  is  one 
of  relaxation. 


GENERAL   PHYSIOLOGY   OF   MUSCLE   TISSUE. 


59 


/ 


Physical  Changes. — The  extensibility  of  muscle  is  increased  during  the 
contraction,  the  same  weight  elongating  the  fibers  to  a  greater  extent  than 
during  rest.  The  elasticity,  or  its  power  of  returning  to  its  original  form 
is  correspondingly  diminished. 

Chemic  Changes. — The  metabolism  of  muscle  during  the  contraction  is 
very  active.  There  is  an  increase  in  the  production  of  carbon  dioxid  and  in 
the  absorption  of  oxygen.  The  muscle  changes  from  an  alkaline  or  neutral 
to  an  acid  reaction,  from  the  development  of  sarcolactic  acid.  The  muscle 
also  becomes  warmer.  The  electric  changes  will  be  treated  of  in  connec- 
tion with  nerves. 

Transmission  of  the  Contraction  Wave. — Normally,  when  a  muscle 
is  stimulated  by  the  nerve  impulse,  the  shortening  and  thickening  of  the 
fibers  begin  at  the  end  organ  and  travel  in  opposite  directions  to  the  ends 
of  the  muscle.  This  change  propagates  itself  in  a  wave-like  manner,  and 
has  been  termed  the  contraction  wave.  If  a  stimulus  be  applied  directly 
to  the  end  of  a  long  muscle,  the  contraction  wave  passes  along  its  entire 
length  to  the  opposite  extremity,  in  virtue  of  the  conductivity  of  muscular 
tissue.  The  rapidity  of  the  propagation  varies  in  different  animals — in  the 
frog,  from  three  to  four  meters  a  second  ;  in  man,  from  ten  to  thirteen 
meters.     The  length  of  the  wave  varies  from  200  to  400  millimeters. 

Graphic  Record  of  a  Muscle  Contraction. — The  changes  in  the 
form  of  a  muscle  during  contraction  and  relaxation  have  been  carefully 


Fig.  4. — Muscle  Curve  Produced  by  a  Single  Induction  Shock  Applied  to 

a  Muscle. — {Landois.) 

a-f.    Abscissa,      a-c.    Ordinate,      a-b.    Period   of  latent   stimulation,      b-d.    Period   of 
increasing  energy,     d-e.  Period  of  decreasing  energy,     e-f.   Elastic  after-vibrations. 


studied  by  recording  the  muscle  movement  by  means  of  an  attached  lever, 
the  end  of  which  is  allowed  to  rest  upon  a  moving  surface.  The  time  rela- 
tions of  all  phases  of  the  muscular  movement  are  obtained  by  placing  be- 
neath the  lever  a  pen  attached  to  an  electromagnet  thrown  into  action  by  a 


60  HUMAN   PHYSIOLOGY. 

tuning-fork  vibrating  in  hundredths  of  a  second.     A  marking  lever  records 
simultaneously  the  moment  of  stimulation. 

Single  Contraction. — When  a  single  electric  induction  shock  is  applied 
to  a  nerve  close  to  the  muscle,  the  latter  undergoes  a  quick  pulsation, 
speedily  returning  to  its  former  condition.  As  shown  by  the  muscle 
curve  (see  Fig.  4),  there  is  between  the  moment  of  stimulation  and  the 
beginning  of  the  contraction  a  short  but  measurable  period,  known  as  the 
latent  period,  during  which  certain  chemic  changes  are  taking  place  pre- 
paratory to  the  exhibition  of  the  muscle  movement.  Even  when  the 
electric  stimulus  is  applied  directly  to  the  muscle,  a  latent  period,  though 
shorter,  is  observable.  The  duration  of  this  period  in  the  skeletal  muscles 
of  the  frog  has  been  estimated  at  0.01  of  a  second ;  but  it  has  been  shown 
by  the  employment  of  more  accurate  methods  and  the  elimination  of  various 
external  influences  to  be  much  less — not  more  than  0.0033  to  0.0025  °f  a 
second. 

The  contraction  follows  the  latent  period.  This  begins  slowly,  rapidly 
reaches  its  maximum,  and  ceases.  This  has  been  termed  the  stage  of  ris- 
ing or  increasing  energy.  The  time  occupied  in  the  stage  of  shortening  is 
about  0.04  of  a  second,  though  this  will  depend  on  the  strength  of  the 
stimulus,  the  load  with  which  the  muscle  is  weighted,  and  the  condition  of 
the  muscle  irritability. 

The  relaxation  immediately  follows  the  contraction.  This  takes  place  at 
first  slowly,  after  which  the  muscle  rapidly  returns  to  its  original  length. 
This  is  the  period  of  falling  or  decreasing  energy,  and  occupies  about  0.05 
of  a  second.  The  whole  duration  of  a  muscle  contraction  occupies,  there- 
fore, about  0.1  of  a  second. 

Residual  or  after-vibrations  are  frequently  seen  which  are  due  to  changes 
in  the  elasticity  of  the  muscle.  The  amplitude  of  the  contraction  depends 
upon  the  condition  of  the  muscle,  the  load,  the  strength  of  stimulus,  etc. 

Contraction  of  Non-striated  Muscle. — The  curve  obtained  by  regis- 
tration of  the  contraction  of  non-striated  muscle  shows  that  it  is  similar  in 
many  respects  to  that  of  the  striated  muscle,  except  that  the  duration  of  the 
former  is  considerably  longer  than  that  of  the  latter. 

Action  of  Successive  Stimuli. — If  a  series  of  successive  stimuli  be 
applied  to  a  muscle,  the  effect  will  be  different  according  to  the  rapidity 
with  which  they  follow  one  another.  If  the  second  stimulus  be  applied  at 
the  termination  of  the  contraction  clue  to  the  first  stimulus,  a  second  con- 
traction follows,  similar  in  all  respects  to  the  first.     A  third  stimulus  pro- 


GENERAL    PHYSIOLOGY   OF   MUSCLE   TISSUE.  61 

duces  a  third  contraction,  and  so  on  until  the  muscle  becomes  exhausted. 
If  the  second  stimulus  be  applied  during  either  of  the  two  periods  of  the 
first  contraction,  the  effects  of  the  two  stimuli  will  be  added  together  and 
the  second  contraction  will  add  itself  to  the  first.  The  maximum  contrac- 
tion is  obtained  when  the  second  stimulus  is  applied  2xff  of  a  second  after 
the  first. 

Tetanus. — When  a  series  of  stimuli  are  applied  to  a  muscle,  following 
one  another  with  median  rapidity,  the  muscle  does  not  get  time  to  relax  in 
ihe  intervals  of  stimulation,  but  remains  in  a  state  of  vibratory  contraction, 
which  may  be  regarded  as  incipient  tetanus,  or  clonus.  As  the  stimulation 
increases  in  frequency,  the  vibrations  become  invisible,  being  completely 
fused  together.  There  is,  nevertheless,  during  the  tetanic  condition  a 
series  of  continuous  contractions  and  relaxations  taking  place.  After  a 
varying  length  of  time  the  muscle  becomes  fatigued,  and  notwithstanding 
the  stimulation,  begins  slowly  to  elongate.  The  number  of  stimuli  neces- 
sary a  second  for  the  production  of  tetanus  varies  in  different  animals — e.g., 
2  to  3  for  muscles  of  the  tortoise ;  io  for  muscles  of  the  rabbit;  15  to  20 
for  the  frog;   70  to  80  for  birds  ;   330  to  340  for  insects. 

A  voluntary  contraction  in  man  may  be  regarded  as  a  state  of 
tetanus,  for  if  the  curve  of  a  voluntary  movement  be  examined,  it  will  be 
found  to  consist  of  intermittent  vibrations.  The  simplest  voluntary  move- 
ment of  a  muscle,  however  rapidly  it  may  take  place,  lasts  longer  than  a 
single  muscular  contraction  due  to  an  induction  shock.  The  most  rapid 
voluntary  contraction  is  the  result  of  from  2.5  to  4  stimulations  a  second, 
and  has  a  duration  of  from  0.041  to  0.064  of  a  second.  A  continuous 
voluntary  contraction  is  an  incomplete  tetanus.  The  number  of  stimuli 
sent  to  the  muscle  is,  on  the  average,  16  to  18  for  rapid  contractions,  8  to 
12  for  slow  contractions. 

The  Production  of  Heat  and  Its  Relation  to  Mechanical  Work. 

— The  transformation  of  energy  which  takes'  place  during  a  muscle  con- 
traction, and  which  is  dependent  upon  chemic  changes  occurring  at  that 
time,  manifests  itself  as  heat  and  mechanical  work.  While  heat  is  being 
evolved  continuously  during  the  passive  condition  of  muscles,  the  amount 
of  heat  is  largely  increased  during  general  muscle  contraction.  A  skeletal 
muscle  of  a  frog, — e.  g.,  the  gastrocnemius, — when  removed  from  the  body, 
shows,  after  tetanization,  an  increase  in  its  temperature  of  from  o.  140  to 
0.180  C,  and  after  a  single  contraction  of  from  0.0010  to  0.0050  C.  While 
every  muscular  contraction  is  attended  by  an  increase  in  heat  production, 


62  HUMAN   PHYSIOLOGY. 

the  amount  so  produced  will  vary  in  accordance  with  certain  conditions — 
e.  g.t  tension,  work  done,  fatigue,  circulation  of  blood,  etc. 

Tension. — The  greater  the  tension  of  a  muscle,  the  greater,  other  con- 
ditions being  equal,  is  the  amount  of  heat  evolved.  When  the  ends  of  a 
muscle  are  fastened  so  that  no  shortening  is  possible  during  stimulation,  the 
maximum  of  heat  production  is  reached.  In  the  tetanic  state  the  great  in- 
crease in  temperature  is  due  to  the  tension  of  antagonistic  and  strongly 
contracted  muscles.  The  evolution  of  heat,  therefore,  bears  a  relation  to 
the  resistance  against  which  the  muscle  is  acting. 

Mechanical  Work. — If  a  muscle  contracts,  loaded  by  a  weight  just  suffi- 
cient to  elongate  it  to  its  original  length,  heat  is  evolved,  but  no  mechanical 
work  is  done,  all  the  energy  liberated  manifesting  itself  as  heat.  When 
the  weight  which  has  been  lifted  is  removed  from  the  muscle  at  the  height 
of  contraction,  external  work  is  done.  In  this  case  the  amount  of  heat 
liberated  is  less,  owing  to  the  work  done,  for  some  of  the  heat  generated  is 
transformed  into  mechanical  motion.  According  to  the  law  of  the  con- 
servation of  energy,  the  amount  of  heat  disappearing  should  correspond  in 
heat  units  to  the  number  of  foot-pounds  produced  by  muscular  contraction. 

Muscle  Sound. — Providing  a  muscle  be  kept  in  a  state  of  tension 
during  its  contraction,  the  intermittent  variations  of  its  tension  cause  the 
muscle  to  emit  an  audible  sound.  If  the  muscle  be  tetanized  by  induction 
shocks,  the  pitch  of  the  sound  corresponds  with  the  number  of  stimuli  a 
second.  A  voluntary  contraction  is  attended  by  a  tone  having  a  vibration 
frequency  of  about  thirty -six  a  second,  which  is,  however,  the  first  overtone 
of  the  true  muscle  tone,  which  is  caused  by  a  contraction  frequency  of 
about  eighteen  a  second.  This  low  tone  is  inaudible,  from  the  small 
number  of  vibrations  a  second. 

Muscle  Fatigue. — Prolonged  or  excessive  muscular  activity  is  followed 
by  a  diminution  in  the  power  of  producing  work  and  by" an  increase  in 
the  duration  of  the  muscular  contractions.  Fatigue  is  accompanied  by  a 
feeling  of  stiffness,  soreness,  and  lassitude,  referable  to  the  muscles  them- 
selves. In  the  early  stages  of  muscular  fatigue  the  contractions  increase 
in  height  and  duration,  to  be  followed  by  a  progressive  decrease  in  height, 
but  an  increase  in  duration,  until  the  muscle  becomes  exhausted.  The 
cause  of  the  fatigue  is  the  production  and  accumulation  of  decomposition 
products,  such  as  phosphoric  acid  and  phosphate  of  potassium,  C02,  etc. 
A  fatigued  muscle  is  rapidly  restored  by  the  injection  of  arterial  blood. 

Work  Done. — Muscles  are  machines  capable  of  doing  a  certain  amount 
\  of  work,  by  which  is  meant  the  raising  of  a  weight  against  gravity  or  the 


SPECIAL   PHYSIOLOGY    OF   MUSCLES.  63 

overcoming  of  some  resistance.  The  work  done  is  calculated  by  multiply- 
ing the  weight  by  the  distance  through  which  it  is  raised.  Thus,  if  a 
muscle  shortens  four  millimeters  and  raises  250  grams,  it  does  work  equal 
to  1,000  milligram-meters,  or  one  gram-meter.  If  a  muscle  contracts  with- 
out being  weighted,  no  work  is  done.  Equally,  when  the  muscle  is  over- 
weighted so  that  it  is  unable  to  contract,  no  work  is  done.  The  amount  of 
work  a  muscle  can  do  will  depend  upon  the  area  of  its  transverse  section, 
the  length  of  its  fibers,  and  the  amount  of  the  weight.  The  amount  of 
work  a  laborer  of  70  kilograms  weight  performs  in  eight  hours  averages 
105,605  kilogram-meters,  or  340.2  foot-tons. 


SPECIAL  PHYSIOLOGY  OF  MUSCLES. 

The  individual  muscles  of  the  axial  and  appendicular  portions  of  the 
body  are  named  with  reference  to  their  shape,  action,  structure,  etc. — e.  g., 
deltoid,  flexor,  penniform,  etc.  In  different  localities  a  group  of  muscles 
having  a  common  function  is  named  in  accordance  with  the  kind  of  motion 
it  produces  or  gives  rise  to — e.  g.,  groups  of  muscles  which  alternately  bend 
or  straighten  a  joint,  or  alternately  diminish  or  increase  the  angular  distance 
between  two  bones,  are  known  respectively  as  flexors  and  extensors  ;  such 
muscle  groups  are  in  association  with  ginglymus  joints.  Muscles  which 
turn  the  bone  to  which  they  are  attached  around  its  own  axis  without  pro- 
ducing any  great  change  of  position  are  known  as  rotators,  and  are  in  as- 
sociation with  the  enarthrodial  or  ball-and-socket  joints.  Muscles  which 
impart  an  angular  movement  of  the  extremities  to  and  from  the  median 
line  of  the  body  are  termed  abductors  and  adductors. 

In  addition  to  the  actions  of  individual  groups  of  muscles  in  causing 
special  movements  in  some  regions,  several  groups  of  muscles  are  coordi- 
nated for  the  accomplishment  of  certain  definite  functions — e.  g.,  muscles 
of  respiration,  mastication,  expression.  The  coordination  of  axial  and 
appendicular  muscles  enables  the  individual  to  assume  certain  postures, 
such  as  standing  and  sitting  ;  to  perform  various  acts  of  locomotion,  as 
walking,  running,  swimming,  etc. 

Levers. — The  function  or  special  mode  of  action  of  individual  muscles 
can  be  understood  only  when  the  bones  with  which  they  are  connected  are 
regarded  as  levers  whose  fulcra  or  fixed  points  lie  in  the  joints  where  the 
movement  takes  place,  and  when  the  muscles  are  considered  as  sources  of 
power  for  imparting  movement  to  the  levers,  with  the  object  of  overcoming 
resistance  or  raising  weights. 


64  HUMAN   PHYSIOLOGY. 

In  mechanics,  levers  of  three  kinds  or  orders  are  recognized,  according 
to  the  relative  positions  of  the  fulcrum  or  axis  of  motion,  the  applied 
power,  and  the  weight  to  be  moved.      (  See  Fig.  5. ) 

In  levers  of  the  first  order  the  fulcrum,  F,  lies  between  the  weight  or 
resistance,  W,  and  the  power  of  moving  force,  P.  The  distance  P-F  is 
known  as  the  power  arm,  the  distance  W-F  as  the  weight  arm.  As  an 
example  of  this  form  of  lever  in  the  human  body  may  be  mentioned  : 

1.  The  elevation  of  the  trunk  from  the  flexed  position.  The  axis  of  move- 
ment, the  fulcrum,  lies  in  the  hip-joint ;  the  weight,  that  of  the  trunk, 
acting  as  if  concentrated  at  its  center  of  gravity,  lies  between  the 
shoulders ;  the  power,  the  contracting  muscles  attached  to  the  tuberosity 
of  the  ischium.  The  opposite  movement  is  equally  one  of  the  first 
order,  but  the  relative  positions  of  P  and  W  are  reversed. 

2.  The  skull  in  its  movements  backward  and  forward  upon  the  atlas. 

In  levers  of  the  second  order  the  weight 

-j.                  ¥  lies  between  the  power  and  the  fulcrum. 

W            a                  ,r>  (l)  -^s  an  illustration  of  this  form  of  lever  may 

»  be  mentioned  : 

p             ^                 1  I.  The   depression  ot   the  lower  jaw,   in 

/\             W                p '  /  which   movement    the    fulcrum    is   the 

_                       t  temporomaxillary  articulation  ;  the  resis- 

w                       r*           (3)  tance,  the  tension  of  the  elevator  mus- 

cles ;  the  power,  the  contraction  of  the 
Fig.  5.  —  The  Three    Orders  .  , 

T  depressor  muscles. 

of  Levers.  r 

2.  The  raising  of  the  body  on  the  toes — 
F  being  the  toes,  W  the  weight  of  the  body  acting  through  the  ankle, 
P  the  gastrocnemius  muscle  acting  upon  the  heel  bone. 
In  levers  of  the  third  order  the  power  is  applied  at  a  point  lying  between 

the  fulcrum  and  the  weight.     As  examples  of  this  form  of  lever  may  be 

mentioned  : 

1.  The  flexion  of  the  forearm — F  being  the  elbow-joint,  P  the  contracting 
biceps  and  brachialis  anticus  muscles  applied  at  their  insertion,  W  the 
weight  of  the  forearm  and  hand. 

2.  The  extension  of  the  leg  on  the  thigh. 

When  levers  are  employed  in  mechanics,  the  object  aimed  at  is  the  over- 
coming of  a  great  resistance  by  the  application  of  a  small  force  acting 
through  a  great  space,  so  as  to  obtain  a  mechanical  advantage.  In  the 
mechanism  of  the  human  body  the  reverse  generally  obtains — viz.,  the 
overcoming  of  a  small  resistance  by  the  application  of  a  great  force  acting 
through  a  small  space.     As  a  result,  there  is  a  gain  in  the  extent  and 


SPECIAL    PHYSIOLOGY   OF   MUSCLES.  65 

rapidity  of  movement  of  the  lever.  The  power,  however,  owing  to  its 
point  of  application,  acts  at  a  great  mechanical  disadvantage  in  many 
instances,  especially  in  levers  of  the  third  order. 

Postures. — Owing  to  its  system  of  joints,  levers,  and  muscles,  the  human 
body  can  assume  a  series  of  positions  of  equilibrium,  such  as  standing  and 
sitting,  to  which  the  name  posture  has  been  given.  In  order  that  the  body 
may  remain  in  a  state  of  stable  equilibrium  in  any  posture,  it  is  essential 
that  the  vertical  line  passing  through  the  center  of  gravity  shall  fall  within 
the  base  of  support. 

Standing  is  that  position  of  equilibrium  in  which  a  line  drawn  through 
the  center  of  gravity  falls  within  the  area  of  both  feet  placed  on  the  ground. 
This  position  is  maintained  : 

1.  By  firmly  fixing  the  head  on  the  top  of  the  vertebral  column  by  the 
action  of  the  muscles  on  the  back  of  the  neck. 

2.  By  making  the  vertebral  column  rigid,  which  is  accomplished  by  the 
longissimus  dorsi  and  the  quadratus  lumborum  muscles.  This  having 
been  accomplished,  the  center  of  gravity  falls  in  front  of  the  tenth  dorsal 
vertebra ;  the  vertical  line  passing  through  this  point  falls  behind  the 
line  connecting  both  hip-joints.  In  consequence,  the  trunk  is  not  balanced 
on  the  hip-joints,  and  would  fall  backward  were  it  not  prevented  by  the 
contraction  of  the  rectus  femoris  muscle  and  ligaments.  At  the  knees 
and  ankles  a  similar  balancing  of  the  parts  above  is  brought  about  by 
the  action  of  various  muscles.  When  the  entire  body  is  in  the  erect  or 
military  position,  the  arms  by  the  sides,  the  center  of  gravity  lies  between 
the  sacrum  and  the  last  lumbar  vertebra,  and  the  vertical  line  touches  the 
ground  between  the  feet  and  within  the  base  of  support. 

Sitting  erect  is  a  condition  of  equilibrium  in  which  the  body  is  balanced 
on  the  tubera  ischii,  when  the  trunk  and  head  together  form  a  rigid  column. 
The  vertical  line  passes  between  the  tubera. 

Locomotion  is  the  act  of  transferring  the  body,  as  a  whole,  through 
space,  and  is  accomplished  by  the  combined  action  of  its  own  muscles. 
The  acts  involved  consist  of  walking,  running,  jumping,  etc. 

Walking  is  a  complicated  act,  involving  almost  all  the  voluntary  muscles 
of  the  body,  either  for  purposes  of  progression  or  for  balancing  the  head  and 
trunk,  and  may  be  defined  as  a  progression  in  a  forward  horizontal  direc- 
tion, due  to  the  alternate  acdon  of  both  legs.  In  walking,  one  leg  becomes 
for  the  time  being,  the  active  or  supporting  leg,  carrying  the  trunk  and 
head  ;  the  other,  the  passive  but  progressive  leg,  to  become  in  turn  the 
active  leg  when  the  foot  touches  the  ground.  Each  leg,  therefore,  is 
alternately  in  an  active  and  a  passive  state. 


66  HUMAN    PHYSIOLOGY. 

Running  is  distinguished  from  walking  by  the  fact  that,  at  a  given  mo- 
ment, both  feet  are  off  the  ground  and  the  body  is  raised  in  the  air. 

While  the  limits  of  a  compend  do  not  permit  of  a  description  of  the  origin, 
insertion,  and  mode  of  action  of  the  individual  muscles  of  the  body,  it  has 
been  thought  desirable  to  call  attention  to  a  few  of  the  principal  muscles 
whose  function  it  is  to  produce  special  forms  of  movement,  as  well  as  loco- 
motion. (See  Fig.  6.)  The  erect  position  is  largely  maintained  by  the 
fixation  of  the  spinal  column  and  the  balancing  of  the  head  upon  its  upper 
extremity  ;  the  former  is  accompanied  by  the  erector  spina  muscle,  named 
from  its  function  and  its  fleshy  continuations,  situated  on  each  side  of  the 
vertebral  column.  Arising  from  the  pelvis  and  lumbar  vertebrae,  this  muscle 
passes  upward,  and  is  attached  by  its  continuations  to  all  the  vertebrae.  Its 
action  is  to  extend  the  vertebral  column  and  to  maintain  the  erect  position. 
The  head  is  balanced  upon  the  top  of  the  vertebral  column  by  the  com- 
bined action  of  the  trapezius  and  suboccipital  muscles  forming  the  nape  of 
the  neck,  and  by  the  sterno-deido-mastoid  muscle.  This  latter  muscle 
arises  from  the  inner  third  of  the  clavicle  and  upper  border  of  the  sternum. 
It  is  inserted  into  the  temporal  bone  just  behind  the  ear.  Its  action  is  to  flex 
the  head  laterally  and  to  rotate  the  face  to  the  opposite  side.  When  both 
muscles  act  simultaneously,  the  head  and  neck  are  flexed  upon  the  thorax. 

The  temporal  and  masseter  muscles,  situated  at  the  side  of  the  head, 
arise  respectively  from  the  temporal  fossa  and  the  zygomatic  arch,  and  are 
inserted  into  the  ramus  of  the  lower  jaw.  Their  action  is  to  close  the 
mouth  and  to  assist  in  mastication.  The  occipito frontalis,  the  orbicularis 
palpebrarum,  and  orbicularis  oris  muscles  are  largely  concerned  in  wrink- 
ling the  forehead,  closing  the  eyes  and  mouth,  and  in  giving  various  ex- 
pressions to  the  face. 

The  deltoid  is  a  thick,  triangular  muscle  covering  the  shoulder-joint. 
Arising  from  the  outer  third  of  the  clavicle,  the  acromial  process,  and  the 
spine  of  the  scapula,  its  fibers  converge  to  be  inserted  into  the  humerus 
just  above  its  middle  point.  Its  action  is  to  elevate  the  arm  through  a  right 
angle.  Owing  to  its  point  of  insertion  it  acts  as  a  lever  of  the  third  order, 
but,  notwithstanding  the  advantageous  point  of  insertion,  it  acts  at  a  con- 
siderable disadvantage,  owing  to  the  obliquity  of  its  direction. 

The  biceps  muscle,  situated  on  the  anterior  aspect  of  the  arm,  arises  from 
the  upper  border  of  the  glenoid  fossa  and  the  coracoid  process,  and  is 
inserted  into  the  radius  just  beyond  the  elbow-joint.  Its  action  is  to  flex 
and  supinate  the  forearm  and  to  place  it  in  the  most  favorable  position  for 
striking  a  blow.  When  the  forearm  is  fixed,  it  assists  in  flexing  the  arm, 
as  in  climbing. 


Fig.  6. — Superficial  Muscles  of  the  Body. 
67 


68  HUMAN   PHYSIOLOGY. 

The  triceps  muscle,  situated  on  the  back  of  the  arm,  arises  from  the 
scapula  and  the  posterior  surface  of  the  humerus,  and  is  inserted  in  the 
olecranon  process  of  the  ulna.  In  its  action  it  directly  antogonizes  the 
biceps,  namely,  extending  the  forearm.  In  so  doing  it  acts  as  a  lever  of 
the  first  order.  The  short  distance  between  the  muscular  insertion  and 
the  fulcrum  causes  it  to  act  at  a  great  mechanical  disadvantage,  but  there  is 
a  corresponding  gain  in  both  speed  and  range  of  movement.  The  muscles 
of  the  forearm  are  very  numerous.  Their  action  is  to  impart  to  the  fore- 
arm and  hand  a  variety  of  movements,  such  as  pronation,  supination, 
flexion,  extension,  rotation,  etc. 

The  pectoralis  major  and  pectoralis  minor  muscles  form  the  fleshy  masses 
of  the  breast.  Arising  from  the  inner  half  of  the  clavicle,  the  side  of  the 
sternum,  and  the  outer  surfaces  of  the  third,  fourth,  and  fifth  ribs  anteriorly, 
the  muscle-fibers  converge  to  be  inserted  into  the  humerus  and  coracoid 
process.  Their  combined  action  is  to  adduct,  flex,  and  rotate  the  arm  in- 
ward, and  to  draw  the  scapula  downward  and  forward,  movements  neces- 
sary to  the  folding  of  the  arms  across  the  chest. 

The  rectus  abdominis  and  the  obliquus  externus  assist  in  forming  the 
abdominal  walls. 

The  glutei  muscles  are  three  in  number,  are  arranged  in  layers,  and  form 
the  fleshy  masses  known  as  the  buttocks.  They  arise  from  the  side  of  the 
pelvis  and  are  attached  to  the  femur  in  the  neighborhood  of  the  great  tro- 
chanter. Their  action  is  to  extend  the  hips,  to  raise  the  body  from  the 
stooping  position,  and  to  assist  in  walking  by  firmly  holding  the  pelvis  on 
the  thigh  while  the  opposite  leg  is  advanced  in  the  forward  direction. 

The  rectus  femoris,  with  its  associates,  the  rectus  internus  and  rectus 
externus  and  the  crureus,  forms  the  fleshy  mass  on  the  anterior  surface  of  the 
thigh.  The  former  arises  from  the  anterior  part  of  the  ilium,  the  latter  from 
the  femur.  Their  common  tendon,  which  is  united  to  the  patella,  is  con- 
tinued as  the  ligamentum  patellae,  which  is  attached  to  the  upper  part  of 
the  tibia.  The  action  of  this  muscular  group  is  to  extend  the  leg,  to  flex 
the  thigh,  and  to  raise  the  entire  weight  of  the  body,  as  in  changing  from 
the  sitting  to  the  erect  position. 

The  biceps  femoris  muscle,  situated  on  the  outer  and  posterior  aspect  of 
the  thigh,  arises  from  the  tuber  ischii,  and  is  inserted  into  the  head  of  the 
fibula. 

The  semimembranosus  and  the  semitendinosus  muscles,  situated  on  the 
inner  and  posterior  aspect  of  the  thigh,  are  inserted  into  the  head  of  the 
tibia.  Their  combined  action  is  to  extend  the  hips  and  to  flex  the  knee. 
Acting  from  below,  they  assist  in  raising  the  body  from  the  stooping  position. 


PHYSIOLOGY   OF   NERVE   TISSUE.  69 

The  gastrocnemius  muscle  forms  the  enlargement  known  as  the  calf  of 
the  leg.  It  arises  by  two  heads  from  the  condyles  of  the  femur.  Its  ten- 
don, the  tendo  Achillis,  is  inserted  into  the  posterior  surface  of  the  heel 
bone.  Its  action  is  to  extend  the  foot  and  to  raise  the  weight  of  the  body 
in  walking  and  running.  On  the  front  of  the  leg  are  numerous  muscles — 
e.  g.,  tibialis  anticus,  peroneus  longus,  etc.,  the  action  of  which  is  to  flex 
the  foot  and  to  antagonize  the  gastrocnemius. 


PHYSIOLOGY   OF    NERVE    TISSUE. 

The  nerve  tissue,  which  unites  and  coSrdinates  the  various  organs  and 
tissues  of  the  body  and  brings  the  individual  into  relationship  with  the 
external  world,  is  arranged  anatomically  into  two  systems,  termed  the 
cerebro-spinal  and  the  sympathetic. 

The  cerebro-spinal  system  consists  of: 

1.  The  brain  and  spinal  cord,  contained  within  the  cavities  of  the  cranium 
and  the  spinal  column  respectively,  and 

2.  The  cranial  and  spinal  nerves. 

The  sympathetic  system  consists  of 

1.  A  double  chain  of  ganglia  situated  on  each  side  of  the  spinal  column 
and  extending  from  the  base  of  the  skull  to  the  tip  of  the  coccyx. 

2.  Various  collections  of  ganglia  situated  in  the  head,  face,  thorax,  abdo- 
men, and  pelvis.  All  these  ganglia  are  united  by  an  elaborate  system 
of  intercommunicating  nerves,  many  of  which  are  connected  with  the 
cerebro-spinal  system. 

HISTOLOGY    OF    NERVE   TISSUE. 

The  Neuron. — The  nerve  tissue  has  been  resolved  by  the  investigations 
of  modern  histologists  into  a  single  morphologic  unit,  to  which  the  term 
neuron  has  been  applied.  The  entire  nervous  system  has  been  shown  to 
be  but  an  aggregate  of  an  infinite  number  of  neurons,  each  of  which  is 
histologically  distinct  and  independent.  Though  having  a  common  origin, 
as  shown  by  embryologic  investigations,  they  have  acquired  a  variety  of 
forms  in  different  parts  of  the  nervous  system  in  the  course  of  development. 
The  old  conception  that  the  nervous  system  consisted  of  two  distinct  histo- 
logic elements,  nerve- cells  and  nerve-fibers,  which  differed  not  only  in 
their  mode  of  origin,  but  also  in  their  properties,  their  relation  to  each 
other,  and  their  functions,  has  been  entirely  disproved. 


70  HUMAN   PHYSIOLOGY. 

The  neuron,  or  neurologic  unit,  is  histologically  a  nerve-cell,  the  sur- 
face of  which  presents  a  greater  or  less  number  of  processes  in  varying 
degrees  of  differentiation.  As  represented  in  figure  7,  the  neuron  may  be 
said  to  consist  of:  (i)  The  nerve-cell,  neurocyte,  or  corpus  ;  (2)  the  axon, 
or  nerve  process;  (3)  the  end  tufts,  or  terminal  branches.  Though  these 
three  main  histologic  features  are  everywhere  recognizable,  they  exhibit 
a  variety  of  secondary  features  in  different  situations  in  accordance  with 
peculiarities  of  function.  Though  the  nerve-cell  and  the  nerve-fiber  are 
but  part  of  the  same  neuron,  it  is  convenient  at  present  to  describe  them 
separately. 

The  Nerve-cell. — The  nerve-cell,  or  body  of  the  neuron,  presents  a 
variety  of  shapes  and  sizes  in  different  portions  of  the  nervous  system. 
Originally  ovoid  in  shape,  it  has  acquired,  in  course  of  development,  pecu- 
liarities of  form  which  are  described  as  pyramidal,  stellate,  pear-shaped, 
spindle-shaped,  etc.  The  size  of  the  cell  varies  considerably,  the  smallest 
having  a  diameter  of  not  more  than  j-^q  of  an  inch,  the  largest  not  more 
than  ¥^q  of  an  inch.  Each  cell  consists  of  granular,  striated  protoplasm, 
containing  a  distinct  vesicular  nucleus  and  a  well-defined  nucleolus.  A 
cell  membrane  has  not  been  observed.  From  the  surface  of  the  adult  cell 
portions  of  the  protoplasm  are  projected  in  various  directions,  which  por- 
tions, rapidly  dividing  and  subdividing,  form  a  series  of  branches,  termed 
dendrites  or  dendrons.  In  some  situations  the  ultimate  branches  of  the 
dendrites  present  short  lateral  processes,  known  as  lateral  buds,  or  gem- 
mules,  which  impart  to  the  branches  a  feathery  appearance.  This  charac- 
teristic is  common  to  the  cells  of  the  cortex,  of  the  cerebrum,  and  of  the 
cerebellum.  The  ultimate  branches  of  the  dendrites,  though  forming  an 
intricate  feltwork,  never  anastomose  with  one  another,  nor  unite  with  den- 
drites of  adjoining  cells.  According  to  the  number  of  axons,  nerve- cells 
are  classified  as  monaxonic,  diaxonic,  polyaxonic.  Most  of  the  cells  of  the 
nervous  system  of  the  higher  vertebrates  are  monaxonic.  In  the  ganglia 
of  the  posterior  or  dorsal  roots  of  the  spinal  and  cranial  nerves,  however, 
they  are  diaxonic.  In  this  situation  the  axons,  emerging  from  opposite 
poles  of  the  cell,  either  remain  separate  and  pursue  opposite  directions,  or 
unite  to  form  a  common  stem,  which  subsequently  divides  into  two  branches, 
which  then  pursue  opposite  directions.  (See  Fig.  7.)  The  nerve-cell 
maintains  its  own  nutrition,  and  presides  over  that  of  the  dendrites  and  the 
axon  as  well.  If  the  latter  be  separated  in  any  part  of  its  course  from  the 
cell,  it  speedily  degenerates  and  dies. 

The  axon,  or  nerve  process,  arises  from  a  cone-shaped  projection  from 


PHYSIOLOGY   OF  NERVE  TISSUE. 


71 


the  surface  of  the  cell,  and  is  the  first  outgrowth  from  its  protoplasm.  At 
a  short  distance  from  its  origin  it  becomes  markedly  differentiated  from  the 
dendrites  which  subsequently  develop.  It  is  characterized  by  a  sharp, 
regular  outline,  a  uniform  diameter,  and  a  hyaline  appearance.  In  struc- 
ture, the  axon  appears  to  consist  of  fine  fibrillce  embedded  in  a  clear,  pro- 
toplasmic  substance.     Shafer   advocates   the  view  that   the   fibrillse    are 


Dendrites. 


Nerve-cell. 


Nerve  process 
or  axon. 


Neurilemma.  —••—••■*• 


Medulla. 


Terminal 
branches. 


Terminal 
branches. 


Neurilemma. 


p   Nerve-cell. 


Fig.  7. 
A.  Efferent  neuron.     B.  Afferent  neuron. 


exceedingly  fine  tubes  filled  with  fluid.  The  axon  varies  in  length  from 
a  few  millimeters  to  100  cm.  In  the  former  instance  the  axon,  at  a  short 
distance  from  its  origin,  divides  into  a  number  of  branches,  which  form  an 
intricate  feltwork  in  the  neighborhood  of  the  cell.  In  the  latter  instance 
the  axon  continues  for  an  indefinite  distance  as  an  individual  structure. 
In  its  course,  however,  especially  in  the  central  nervous  system,  it  gives 
off  a  number  of  collateral  branches,  which  possess  all  its  histologic  features. 


72  HUMAN  PHYSIOLOGY. 

The  long  axons  seem  to  bring  the  body  of  the  cell  into  direct  relation  with 
peripheral  organs,  or  with  more  or  less  remote  portions  of  the  nervous 
system,  thus  constituting  association  or  commissural  fibers. 

The  more  or  less  elongated  axon  becomes  invested,  as  a  rule,  at  a  short 
distance  from  the  cell  with  nucleated  oblong  cells,  which  subsequently 
become  modified  and  constitute  a  medullary  or  myelin  sheath.  This  is  in- 
vested by  a  thin,  cellular  membrane — the  neurilemma.  These  three  struc- 
tures thus  constitute  what  is  known  as  a  medullated  nerve-fiber.  In  the 
central  nervous  system  the  outer  sheath  is  frequently  absent.  In  the  sym- 
pathetic system  the  myelin  is  frequently  absent,  though  the  axon  is  inclosed 
by  the  neurilemma,  thus  constituting  a  non-medullated  nerve-fiber. 

The  end  tufts  or  terminal  organs  are  formed  by  the  splitting  of  the  axon 
into  a  number  of  filaments,  which  remain  independent  of  one  another  and 
are  free  from  the  medullary  investment.  The  histologic  peculiarities  of 
the  terminal  organs  vary  in  different  situations,  and  in  many  instances  are 
quite  complex  and  characteristic.  In  peripheral  organs,  as  muscles, 
glands,  blood-vessels,  skin,  mucous  membrane,  the  tufts  are  in  direct  or- 
ganic connection  with  their  cellular  elements.  In  the  central  nervous 
system  the  tufts  are  in  more  or  less  intimate  relation  with  the  dendrites  of 
adjacent  neurons. 

Nerve-fibers. — The  axons  with  their  secondary  investments  together 
constitute  the  nerve-fibers,  and  according  as  they  possess  or  do  not  possess 
the  medullary  sheath,  they  may  be  divided  into  two  groups — viz.,  medul- 
lated and  non-medullated  fibers. 

Medullated  Nerve-fibers. — These  consist  for  the  most  part  of  three 
distinct  structures  : 

1.  An  external  investing  sheath,  tubular  in  shape,  termed  the  neurilemma. 

2.  An  intermediate  semifluid  substance — the  medulla  or  myelin. 

3.  An  internal  dark  thread — the  axis-cylinder. 

The  neurilemma  is  a  thin,  transparent,  homogeneous  membrane  closely 
adherent  to  the  medulla.  Owing  to  its  colorless  appearance,  it  can  be  seen 
only  with  difficulty  in  the  recent  condition.  When  treated  with  various 
reagents,  it  becomes  distinct.  Physically,  it  is  quite  resistant  and  elastic. 
Its  function  is  doubtless  that  of  a  protective  agent  to  the  structures 
within. 

The  medulla,  myelin,  or  white  substance  of  Schwann  completely  fills 
the  neurilemma  and  closely  invests  the  axis-cylinder.  In  the  recent  con- 
dition the  medulla  is  clear,  homogeneous,  semifluid,  and  highly  refracting. 
In  composition  it  is  oleaginous.     When  the  nerve  is  treated  with  various 


PHYSIOLOGY   OF   NERVE   TISSUE.  73 

reagents  which  alter  its  composition,  the  medulla  becomes  opaque  and  im- 
parts to  the  nerve  a  white,  glistening  appearance.  The  function  of  the 
medulla  is  quite  unknown. 

At  intervals  of  about  seventy-five  times  its  diameter  the  medullated 
nerve-fiber  undergoes  a  remarkable  diminution  in  size,  due  to  an  interrup- 
tion of  the  medullary  substance,  so  that  the  neurilemma  lies  directly  on  the 
axis-cylinder.  These  constrictions,  or  nodes  of  Ranvier,  taking  their  name 
from  their  discoverer,  occur  at  regular  intervals  along  the  course  of  the 
nerve,  separating  it  into  a  series  of  segments.  The  portion  between  the 
nodes  is  termed  the  internodal  segment.  It  has  been  suggested  that  in 
consequence  of  the  absence  of  the  myelin  at  these  nodes,  a  free  exchange 
of  nutritive  material  and  decomposition  products  can  take  place  between 
the  axis-cylinder  and  the  surrounding  plasma. 

The  axis-cylinder,  or  axon,  the  direct  outgrowth  of  the  nerve-cell,  is  the 
most  essential  element  of  the  nerve-fiber,  as  it  alone  is  uniformly  continuous 
throughout.  In  the  natural  condition  it  is  transparent  and  invisible  ;  but 
when  treated  with  proper  reagents,  it  presents  itself  as  a  'pale,  granular, 
flattened  band,  more  or  less  solid  and  somewhat  elastic.  It  is  albuminous 
in  composition.  With  high  magnification  the  axis  presents  a  longitudinal 
striation,  indicating  a  fibrillar  structure.  The  fibrillar  appear  to  be  united 
by  an  intervening  cement  substance. 

Non-medullated  Nerve-fibers. — These  consist,  for  the  most  part, 
only  of  the  axis-cylinder,  though  in  some  portions  of  the  nervous  system  a 
neurilemma  is  also  present.  Though  much  less  abundant  than  the  former 
variety,  they  are  distributed  largely  throughout  the  nervous  system,  but  are 
particularly  abundant  in  the  sympathetic  system.  Owing  to  the  absence  of 
a  medulla,  they  present  a  rather  pale  or  grayish  appearance. 

Structure  of  Nerve  Trunks. — After  their  emergence  from  the  brain 
and  spinal  cord,  the  nerve-fibers  become  bound  together,  by  connective 
tissue,  into  the  form  of  continuous  bundles,  which  connect  the  brain  and 
cord  with  all  the  remaining  structures  of  the  body.  The  bundles  are  tech- 
nically known  as  nerve  trunks  or  nerves.  Each  nerve  is  invested  by  a 
thick  layer  of  lamellated  connective  tissue,  known  as  the  epineurhim. 
A  transverse  section  of  a  nerve  shows  (see  Fig.  8)  that  it  is  made  up  of  a 
number  of  small  bundles  of  fibers,  each  of  which  possesses  a  separate 
investment  of  connective  tissue — the  perineurium.  Within  this  membrane 
the  nerve-fibers  are  supported  by  a  fine  stroma — the  endoneurium.  After 
pursuing  a  longer  or  shorter  course,  the  nerve  trunk  gives  off  branches, 
which  interlace  very  freely  with  neighboring  branches,  forming  plexuses, 


74 


HUMAN   PHYSIOLOGY. 


the  fibers  of  which  are  distributed  to  associated  organs  and  regions  of  the 
body.  From  their  origin  to  their  termination,  however,  nerve-fibers  retain 
their  individuality,  and  never  become  blended  with  adjoining  fibers. 

As  nerves  pass  from  their  origin  to  their  peripheral  terminations,  they 
give  off  a  number  of  branches,  each  of  which  becomes  invested  with  a 
lamellated  sheath — an  offshoot  from  that  investing  the  parent  trunk.  This 
division  of  nerve  bundles  and  sheath  continues  throughout  all  the  branch- 
ings down  to  the  ultimate  nerve-fibers,  each  of  which  is  surrounded  by  a 


Fig.  8. — Transverse  Section  of  a  Nerve  (Median). 
ep    Epineurium.    pe.  Perineurium,     ed.  Endoneurium. 


sheath  of  its  own,  consisting  of  a  single  layer  of  endothelial  cells.  This 
delicate  transparent  membrane,  the  sheath  of  Henle,  is  separated  from  the 
nerve-fiber  by  a  considerable  space,  in  which  is  contained  lymph  destined 
for  the  nutrition  of  the  fiber.  Near  their  ultimate  terminations  the  nerve- 
fibers  themselves  undergo  division,  so  that  a  single  fiber  may  give  origin  to 
a  number  of  branches,  each  of  which  contains  a  portion  of  the  parent  axis- 
cylinder  and  myelin. 


PHYSIOLOGY  OF   NERVE  TISSUE.  75 

CLASSIFICATION  OF  NERVES. 

Nerves  are  channels  of  communication  between  the  brain  and  spinal 
cord,  on  the  one  hand,  and  the  muscles,  glands,  blood-vessels,  skin,  mucous 
membrane,  viscera,  etc.,  on  the  other.  Some  of  the  nerve-fibers  serve  for 
the  transmission  of  nerve  energy  or  nerve  impulses  from  the  brain  and 
spinal  cord  to  certain  peripheral  organs,  and  so  increase  or  retard  their 
activities ;  others  serve  for  the  transmission  of  nerve  energy  from  certain 
peripheral  organs  to  the  brain  and  spinal  cord,  which  gives  rise  to  sensa- 
tions or  other  modes  of  nerve  activity.  The  former  are  termed  efferent  or 
centrifugal  nerves  ;  the  latter  are  termed  afferent  or  centripetal  nerves. 

The  efferent  nerves  may  be  classified,  in  accordance  with  the  charac- 
teristic form  of  activity  to  which  they  give  rise,  into  several  groups,  as 
follows  : 

1.  Muscular  ox  motor  nerves,  those  which  convey  nerve  energy  or  nerve 
impulses  to  muscles  and  give  rise  to  muscular  contraction. 

2.  Glandular  or  secretory  nerves,  those  which  convey  nerve  impulses  to 
glands,  and  cause  the  formation  of  the  secretion  peculiar  to  the  gland. 

3.  Vascular  or  vaso-motor  nerves,  those  which  convey  nerve  impulses  to 
blood-vessels,  and  cause,  either  by  stimulation  or  inhibition  of  the  mech- 
anism of  their  walls,  a  contraction  (vaso- constrictors)  or  dilatation  (vaso- 
dilators) of  the  vessel. 

4.  Inhibitory  nerves,  those  conveying  nerve  impulses  that  cause  a  slowing 
or  complete  cessation  of  the  rhythmic  action  of  organs. 

5.  Accelerator  nerves,  those  conveying  impulses  that  cause  an  increase  in 
the  rhythmic  action  of  certain  organs. 

The  afferent  nerves  may  also  be  classified,  in  accordance  with  the 
character  of  the  sensations  or  other  modes  of  nerve  activity  to  which  they 
give  rise,  into  several  groups,  as  follows  : 

1.  Sensorifacient  nerves,  those  conveying  nerve  impulses  that  give  rise  in 
the  brain  to  conscious  sensations.     They  may  be  subdivided  into — 
[a)  Nerves  of  special  sense — e.g.,  olfactory,  optic,  auditory,  gusta- 
tory, tactile,   thermal,  sensory,  muscle — those  which  give  rise  to 
olfactory,  optic,  auditory,  gustatory,  tactile,   thermic,  painful,  and 
muscle  sensations. 
(£)  Nerves  of  general  sense — e.  g.,  the  visceral  afferent  nerves — those 
which  give  rise  normally  to  vague  and  scarcely  perceptible  sensa- 
tions, such  as  the  general  sensations  of  well-being  or  discomfort, 
hunger,  thirst,  fatigue,  sex,  want  of  air,  etc. 


76  HUMAN    PHYSIOLOGY. 

2.  Reflex  nerves,  those  which  convey  nerve  impulses  to  the  nerve  centers 
and  cause  a  discharge  and  transmission  of  nerve  impulses  outward 
through  efferent  nerves  to  muscles,  glands,  or  blood-vessels,  and  thus 
influence  their  activity.  It  is  quite  probable  that  one  and  the  same 
nerve  may  subserve  both  sensational  and  reflex  action,  owing  to  the  col- 
lateral branches  which  are  given  off  from  the  posterior  roots  as  they 
ascend  the  posterior  column  of  the  cord. 

3.  Inhibitory  nerves,  those  which  are  capable  reflexly  of  retarding  or  in- 
hibiting the  activity  of  either  nerve  centers  or  peripheral  organs. 

The  Terminal  Endings  of  Nerves. — The  efferent  nerves,  as  they 
approach  their  ultimate  terminations,  lose  both  the  neurilemma  and  medul- 
lary sheath.  The  axis-cylinder  then  divides  into  a  number  of  tufts  or 
branches,  which  become  directly  and  intimately  connected  with  the  tissue 
cells.  The  particular  mode  of  termination  varies  in  different  situations. 
These  terminations  are  generally  spoken  of  as  "  end  organs" 

In  the  skeletal  muscles  the  nerve-fiber  loses  both  neurilemma  and  myelin 
sheath  at  the  point  where  it  comes  into  contact  with  the  muscle-fiber. 
After  penetrating  the  sarcolemma,  the  axis- cylinder  breaks  up  into  small 
branches  with  bulbous  extremities,  forming  the  so-called  "motor  plate," 
which  rests  directly  on  a,  disc  of  granular  material  containing  oval,  vesic- 
ular nuclei.     Each  muscle-fiber  possesses  an  individual  end-plate. 

In  the  visceral  muscles  the  terminal  nerve-fibers  form  a  plexus  around  the 
muscle-fibers,  and  become  organically  connected  with  them.  In  the 
glands  the  nerve-fibers  have  been  traced  directly  to  their  secreting  cells. 
The  exact  mode  of  their  termination  and  connection  with  the  cells  has  not 
been  clearly  determined. 

The  afferent  nerves,  as  they  approach  their  peripheral  terminations,  be- 
come connected  in  like  manner  with  end  organs,  which,  in  some  instances, 
are  extremely  complex,  such  as  those  found  in  the  eye  (retina),  the  internal 
ear,  the  nose,  and  the  tongue.  (A  consideration  of  these  end  organs  will 
be  found  in  the  chapters  devoted  to  the  organs  of  which  they  form  a  part. ) 
The  end  organs  of  the  skin  and  mucous  membranes  present  a  variety  of 
forms,  and  may  be  classified  as  follows  : 

1 .  Free  endings  in  the  epithelium  of  the  skin,  mucous  membrane,  and  cornea. 

2.  Tactile  cells  of  Merkel  in  the  epidermis. 

2.  Tactile  corpuscles  in  the  papillae  of  the  true  skin. 

4.  Pacinian  corpuscles  found  attached  to  the  nerves  of  the  hands  and  feet, 
to  the  intercostal  nerves,  and  to  nerves  in  other  situations. 

5.  End  bulbs  of  Krause  in  the  conjunctiva,  penis,  clitoris,  etc. 


PHYSIOLOGY    OF    NERVE   TISSUE.  77 

The  end  organs  of  the  afferent  nerves  are  specialized,  highly  irritable 
structures  placed  between  the  nerve-fibers  and  the  surface  of  the  body. 
They  are  especially  adapted  for  the  reception  of  those  external  forces  tech- 
nically known  as  stimuli,  and  for  the  liberation  of  energy  capable  of  excit- 
ing the  nerve-fiber  to  activity. 

Relation  of  Peripheral  Nerves  to  the  Central  Nervous  System. — 
The  nerves  in  connection  with  the  spinal  cord  are  thirty-one  in  number  on 
each  side  and  have  two  roots  of  origin,  an  anterior  and  a  posterior,  which 
arise  from  the  anterior  and  posterior  surfaces  of  the  cord  respectively. 
They  are  more  properly  termed  ventral  and  dorsal  roots.  The  dorsal 
roots  present,  near  their  entrance  into  the  cord,  an  enlargement  termed  a 
ganglion.  Beyond  the  spinal  canal  these  two  roots  unite  to  form  the 
ordinary  spinal  nerve.  Some  of  the  nerves  in  connection  with  the  base 
of  the  brain  also  present  a  ganglionic  enlargement,  and  may,  therefore,  be 
regarded  physiologically  as  dorsal  nerves,  while  others  may  be  regarded  as 
ventral  nerves. . 

Experimentally,  it  has  been  determined  that  the  anterior  or  ventral  roots 
contain  all  the  efferent  fibers,  the  posterior  or  dorsal  roots  all  the  afferent 
fibers.     The  proofs  in  support  of  this  view  are  as  follows  : 

Stimulation  of  the  ventral  roots  produces  : 

1.  Convulsive  movements  of  muscles. 

2.  The  formation  of  a  secretion  in  glands. 

3.  Changes  in  the  caliber  of  blood-vessels. 

4.  Inhibition  of  the  rhythmic  activity  of  certain  organs. 
Divisions  of  these  roots  is  -followed  by  : 

1.  Loss  of  muscular  movement  (paralysis  of  motion). 

2.  Cessation  of  secretion. 

3.  Cessation  of  vascular  changes. 
Stimulation  of  the  dorsal  roots  causes  : 

1.  Reflex  activities. 

2.  Conscious  sensations. 

3.  Inhibition  of  the  rhythmic  activity  of  certain  organs. 
Division  of  these  roots  is  followed  by  : 

1.  Loss  of  reflex  activities,  and 

2.  Loss  of  sensation  in  all  parts  to  which  they  are  distributed. 

The  ventral  roots  are,  therefore,  efferent  in  function,  transmitting  nerve 
impulses  from  the  nerve  centers  to  the  periphery.  The  dorsal  roots  are 
afferent  in  function,  transmitting  nerve  impulses  from  the  general  periphery 
to  the  nerve  centers. 


78 


HUMAN   PHYSIOLOGY. 


Development  and  Nutrition  of  Nerves. — The  efferent  nerve- 
fibers,  which  constitute  some  of  the  cranial  nerves  and  all  the  ventral  roots 
of  the  spinal  nerves,  have  their  origin  in  cells  located  in  the  gray  matter 
beneath  the  aqueduct  of  Sylvius,  beneath  the  floor  of  the  fourth  ventricle 
and  in  the  anterior  horns  of  the  gray  matter  of  the  spinal  cord.  These 
cells  are  the  modified  descendants  of  independent,  oval,  pear-shaped  cells 
— the  neuroblasts — which  migrate  from  the  medullary  tube.  As  they 
approach  the  surface  of  the  cord  their  axons  are  directed  toward  the 
ventral  surface,  which  eventually  they  pierce.     Emerging  from  the  cord, 


Posterior 
Jloot 


Gcuuflian, 


rrierwr 
£oot 


Fig.  9. — Diagram  Showing  the  Mode  of  Origin  of  the  Ventral  and 

Dorsal  Roots. 


the  axions  continue  to  grow,  and  become  invested  with  the  myelin  sheath 
and  neurilemma,  thus  constituting  the  ventral  roots. 

The  afferent  nerve-fibers,  which  constitute  some  of  the  cranial  nerves 
and  all  the  dorsal  roots  of  the  spinal  nerves,  develop  outside  of  the  central 
nervous  system  and  only  subsequently  become  connected  with  it.  ( See  Fig. 
9. )  At  the  time  of  the  closure  of  the  medullary  tube  a  band  or  ridge  of 
epithelial  tissue  develops  near  the  dorsal  surface,  which,  becoming  seg- 
mented, moves  outward  and  forms  the  rudimentary  spinal  ganglia.  The  cells 
in  this  situation  develop  two  axons,  one  from  each  end  of  the  cell,  which 


PHYSIOLOGY    OF    NERVE   TISSUE.  79 

pass  in  opposite  directions,  one  toward  the  spinal  cord,  the  other  toward 
the  periphery.  In  the  adult  condition  the  two  axons  shift  their  position, 
unite,  and  form  a  T-shaped  process,  after  which  a  division  into  two  branches 
again  takes  place.  In  the  ganglia  of  all  the  sensoricranial  and  sensori- 
spinal  nerves  the  cells  have  this  histologic  peculiarity. 

Nerve  Degeneration. — If  any  one  of  the  cranial  or  spinal  nerves  be 
divided  in  any  portion  of  its  course,  the  part  in  connection  with  the 
periphery  in  a  short  time  exhibits  certain  structural  changes,  to  which  the 
term  degeneration  is  applied.  The  portion  in  connection  with  the  brain  or 
cord  retains  its  normal  condition.  The  degenerative  process  begins  simul- 
taneously throughout  the  entire  course  of  the  nerve,  and  consists  in  a  disin- 
tegration and  reduction  of  the  medulla  and  axis-cylinder  into  nuclei,  drops 
of  myelin,  and  fat,  which  in  time  disappear  through  absorption,  leaving  the 
neurilemma  intact.  Coincident  with  these  structural  changes  there  is  a 
progressive  alteration  and  diminution  in  the  excitability  of  the  nerve. 
Inasmuch  as  the  central  portion  of  the  nerve,  which  retains  its  connection 
with  the  nerve- cell,  remains  histologically  normal,  it  has  been  assumed 
that  the  nerve-cells  exert  over  the  entire  course  of  the  nerve-fibers  a  nutri- 
tive or  a  trophic  influence.  This  idea  has  been  greatly  strengthened  since 
the  discovery  that  the  axis-cylinder,  or" the  axon,  has  its  origin  in  and  is  a 
direct  outgrowth  of  the  cell.  When  separated  from  the  parent  cell,  the 
fiber  appears  to  be  incapable  of  itself  of  maintaining  its  nutrition. 

The  relation  of  the  nerve-cells  to  the  nerve-fibers,  in  reference  to  their 
nutrition,  is  demonstrated  by  the  results  which  follow  section  of  the 
ventral  and  dorsal  roots  of  the  spinal  nerves.  If  the  anterior  root 
alone  be  divided,  the  degenerative  process  is  confined  to  the  peripheral 
portion,  the  central  portion  remaining  normal.  If  the  posterior  root  be 
divided  on  the  peripheral  side  of  the  ganglion,  degeneration  takes  place 
only  in  the  peripheral  portion  of  the  nerve.  If  the  root  be  divided  between 
the  ganglion  and  the  cord,  degeneration  takes  place  only  in  the  central 
portion  of  the  root.  From  these  facts  it  is  evident  that  the  trophic  centers 
for  the  ventral  and  dorsal  roots  lie  in  the  spinal  cord  and  spinal  nerve 
ganglia,  respectively,  or,  in  other  words,  in  the  cells  of  which  they 
are  an  integral  part.  The  structural  changes  which  nerves  undergo  after 
separation  from  their  centers  are  degenerative  in  character,  and  the 
process  is  usually  spoken  of,  after  its  discoverer,  as  the  Wallerian  degen- 
eration. 

When  the  degeneration  of  the  efferent  nerves  is  completed,  the  structures 
to  which  they  are  distributed,  especially  the  muscles,  undergo  an  atrophic 
or  fatty  degeneration,  with  a  change  or  loss  of  their  irritability.     This  is, 


80  HUMAN    PHYSIOLOGY. 

apparently,  not  to  be  attributed  merely  to  inactivity,  but  rather  to  a  loss  of 
nerve  influences,  inasmuch  as  inactivity  merely  leads  to  atrophy  and  not  to 
degeneration. 

Reactions  of  Degeneration.  —  In  consequence  of  the  degeneration 
and  changes  in  irritability  which  occur  in  nerves  and  muscles  when  sepa- 
rated, either  experimentally  or  as  the  result  of  disease,  the  response  of 
these  structures  to  the  induced  and  the  make -and- break  of  the  constant 
currents  differs  from  that  observed  in  the  physiologic  condition.  The  facts 
observed  under  the  application  of  these  two  forms  of  electricity  are  of  the 
greatest  importance  in  the  diagnosis  and  therapeutics  of  the  precedent 
lesions.  The  principal  difference  of  behavior  is  observed  in  the  muscles, 
which  exhibit  a  diminished  or  abolished  excitability  to  the  induced  current, 
while  at  the  same  time  manifesting  an  increased  excitability  to  the  constant 
current ;  so  much  so  is  this  the  case  that  a  closing  contraction  is  just  as 
likely  to  occur  at  the  positive  as  at  the  negative  pole.  This  peculiarity  of 
the  muscle  response  is  termed  the  reaction  of  degeneration.  The  syn- 
chronous diminished  excitability  of  the  nerves  is  the  same  for  either  cur- 
rent. The  term  "partial  reaction  of  degeneration"  is  used  when  there 
is  a  normal  reaction  of  the  nerves,  with  the  degenerative  reaction  of  the 
muscles.     This  condition  is  observed  in  progressive  muscular  atrophy. 

Reflex  Action. — Inasmuch  as  many  of  the  muscle  movements  of  the 
body,  as  well  as  the  formation  and  discharge  of  secretions  from  glands, 
variations  in  the  caliber  of  blood-vessels,  inhibition  and  acceleration  in  the 
activity  of  various  organs,  are  the  result  of  stimulations  of  the  terminal 
organs  of  afferent  nerves,  they  are  termed,  for  convenience,  reflex  actions, 
and,  as  they  take  place  independently  of  the  brain  or  of  volitional  impulses, 
they  are  also  termed  involuntary  actions.  As  many  of  the  processes  to  be 
described  in  succeeding  chapters  are  of  this  character,  requiring  for  their 
performance  the  cooperation  of  several  organs  and  tissues  associated 
through  the  intermediation  of  the  nervous  system,  it  seems  advisable  to 
consider  briefly,  in  this  connection,  the  parts  involved  in  a  reflex  action,  as 
well  as  their  mode  of  action.  As  shown  in  figure  io,  the  necessary  struc- 
tures are  as  follows  : 

1.  A  sentient  surface,  skin,  mucous  membrane,  sense  organ,  etc. 

2.  An  afferent  nerve. 

3.  An  emissive  cell,  from  which  arises 

4.  An  efferent  nerve,  distributed  to  a  responsive  organ,  as 

5.  Muscle,  gland,  blood-vessel,  etc. 

Such  a  combination  of  structures  constitutes  a  reflex  mechanism  or  arc, 


PHYSIOLOGY   OK    NERVE   TISSUE.  81 

the  nerve  portion  of  which  is  composed  of  but  two  neurons — an  afferent 
and  an  efferent.  An  arc  of  this  simplicity  would  of  necessity  subserve 
but  a  simple  movement.  The  majority  of  reflex  activities,  however,  are 
extremely  complex,  and  involve  the  cooperation  and  coordination  of  a 
number  of  structures  frequently  situated  at  distances  more  or  less  remote 
from  one  another.  This  implies  that  a  number  of  neurons  are  associated 
in  function.  The  afferent  neurons  are  brought  into  relation  with  the  den- 
drites of  the  efferent  neurons  by  the  end  tufts  of  the  collateral  branches, 


/ 


Fig.  io. — Diagram  Illustrating  Reflex  Action. — {Kirke.) 
S.  Sentient  surface  from  which  proceeds  the  afferent  nerve.     M.  C.   Motor  or  emissive 
cell  giving  origin  to  efferent  nerve  which  terminates  in  M.     31.  Motor  organ.     G. 
Ganglion  cell  on  afferent  nerve 

which  may  extend  for  some  distance  up  and  down  the  cord  before  passing 
into  the  various  segments. 

For  the  excitation  of  a  reflex  action  it  is  essential  that  the  stimulus 
applied  to  the  sentient  surface  be  of  an  intensity  sufficient  to  develop  in  the 
terminals  of  the  afferent  nerve  a  series  of  nerve  impulses,  which,  traveling 
inward,  will  be  distributed  to  and  received  by  the  dendrites  of  the  emissive 
or  motor  cell.  With  the  reception  of  these  impulses  there  is  apparently  a 
disturbance  of  the  equilibrium  of  its  molecules,  a  liberation  of  energy, 
and,    in   consequence,  a  transmission    outward  of  impulses   through    the 


82  HUMAN   PHYSIOLOGY. 

efferent  nerve  to  muscle,  gland,  or  blood-vessel,  separately  or  collectively, 
with  the  production  of  muscular  contraction,  glandular  secretion,  vascular 
dilatation  or  contraction,  etc.  The  reflex  actions  take  place,  for  the  most 
part,  through  the  spinal  cord  and  medulla  oblongata,  which,  in  virtue  of 
their  contained  centers,  coordinate  the  various  organs  and  tissues  concerned 
in  the  performance  of  the  organic  functions.  The  movements  of  mastication ; 
the  secretion  of  saliva  ;  the  muscular,  glandular,  and  vascular  phenomena 
of  gastric  and  intestinal  digestion  ;  the  vascular  and  respiratory  movements  ; 
the  mechanism  of  micturition,  etc.,  are  illustrations  of  reflex  activity. 

PHYSIOLOGIC    PROPERTIES    OF   NERVES. 

Nerve  Irritability  or  Excitability  and  Conductivity. — These  terms 
are  employed  to  express  that  condition  of  a  nerve  which  enables  it  to  de- 
velop and  to  conduct  nerve  impulses  from  the  center  to  the  periphery,  from 
the  periphery  to  the  center,  in  response  to  the  action  of  stimuli.  A  nerve 
is  said  to  be  excitable  or  irtritable  as  long  as  it  possesses  these  capabilities 
or  properties.  For  the  manifestation  of  these  properties  the  nerve  must 
retain  a  state  of  physical  and  chemic  integrity  ;  it  must  undergo  no  change 
in  structure  or  chemic  composition.  The  irritability  of  an  efferent  nerve  is 
demonstrated  by  the  contraction  of  a  muscle,  by  the  secretion  of  a  gland,  or 
by  a  change  in  the  caliber  of  a  blood-vessel,  whenever  a  corresponding  nerve 
is  stimulated.  The  irritability  of  an  afferent  nerve  is  demonstrated  by  the 
production  of  a  sensation  or  a  reflex  action  whenever  it  is  stimulated. 
The  irritability  of  nerves  continues  for  a  certain  period  of  time  after  separa- 
tion from  the  nerve  centers  and  even  after  the  death  of  the  animal,  varying 
in  different  classes  of  animals.  In  the  warm-blooded  animals,  in  which 
the  nutritive  changes  take  place  with  great  rapidity,  the  irritability  soon 
disappears — a  result  due  to  disintegrative  changes  in  the  nerve,  caused  by 
the  withdrawal  of  the  blood-supply.  In  cold-blooded  animals,  on  the 
contrary,  in  which  the  nutritive  changes  take  place  relatively  slowly,  the 
irritability  lasts,  under  favorable  conditions,  for  a  considerable  time. 
Other  tissues  besides  nerves  possess  irritability,  that  is,  the  property  of  re- 
sponding to  the  action  of  stimuli — e.  g.,  glands  and  muscles,  which 
respond  by  the  production  of  a  secretion  or  a  contraction. 

Independence  of  Tissue  Irritability. — The  irritability  of  nerves  is 
distinct  and  independent  of  the  irritability  of  muscles  and  glands,  as  shown 
by  the  fact  that  it  persists  in  each  a  variable  length  of  time  after  their  his- 
tologic connections  have  been  impaired  or  destroyed  by  the  introduction  of 
various  chemic  agents  into  the  circulation.     Curara,  for  example,  induces  a 


PHYSIOLOGY   OF   NERVE   TISSUE.  83 

state  of  complete  paralysis  by  modifying  or  depressing  the  conductivity  of 
the  end  organs  of  the  nerves  just  where  they  come  in  contact  with  the 
muscles  without  impairing  the  irritability  of  either  nerve  trunks  or  muscles. 
Atropin  induces  complete  suspension  of  glandular  activity  by  impairing  the 
terminal  organs  of  the  secretory  nerves  just  where  they  come  into  relation 
with  the  gland-cells,  without  destroying  the  irritability  of  either  gland  or 
nerve. 

Stimuli  of  Nerves. — Nerves  do  not  possess  the  power  of  spontaneously 
generating  and  propagating  nerve  impulses  ;  they  can  be  aroused  to  activity 
only  by  the  action  of  an  extraneural  stimulus.  In  the  living  condition 
the  stimuli  capable  of  throwing  the  nerve  into  an  active  condition  act  for 
the  most  part  on  either  the  central  or  peripheral  end  of  the  nerve.  In  the 
case  of  motor  nerves  the  stimulus  to  the  excitation,  originating  in  some 
molecular  disturbance  in  the  nerve-cells,  acts  upon  the  nerve-fibers  in  con-/ 
nection  with  them.  In  the  case  of  sensory  or  afferent  nerves  the  stimuli  act; 
upon  the  peculiar  end  organs  with  which  the  sensory  nerves  are  in  connec- 
tion, which  in  turn  excite  the  nerve-fibers.  Experimentally,  it  can  be 
demonstrated  that  nerves  can  be  excited  by  a  sufficiently  powerful  stimulus 
applied  in  any  part  of  their  extent. 

Nerves  respond  to  stimulation  according  to  their  habitual  function  ;  thus, 
stimulation  of  a  sensory  nerve,  if  sufficiently  strong,  results  in  the  sensation 
of  pain  ;  of  the  optic  nerve,  in  the  sensation  of  light ;  of  a  motor  nerve,  in 
conti  action  of  the  muscle  to  which  it  is  distributed  ;  of  a  secretory  nerve, 
in  the  activity  of  the  related  gland,  etc.  It  is,  therefore,  evident  that  pecu- 
liarity of  nervous  function  depends  neither  upon  any  special  construction 
or  activity  of  the  nerve  itself,  nor  upon  the  nature  of  the  stimulus,  but 
entirely  upon  the  peculiarities  of  its  central  and  peripheral  end  organs. 

Nerve  stimuli  may  be  divided  into — 

1.  General  stimuli,  comprising  those  agents  which  are  capable  of  exciting 
a  nerve  in  any  part  of  its  course. 

2.  Special  stimuli,  comprising  those  agents  which  act  upon  nerves  only 
through  the  intermediation  of  the  end  organs. 

General  stimuli  : 

1.  Mechanical  :  as  from  a  blow,  pressure,  tension,  puncture,  etc. 

2.  Thermal  :    heating   a   nerve    at  first   increases   and   then  decreases  its 
excitability. 

3.  Chemic  :  sensory  nerves  respond  somewhat  less  promptly  than  motor 
nerves  to  this  form  of  irritation. 

4.  Electric  :  either  the  constant  or  interrupted  current. 


84  HUMAN    PHYSIOLOGY. 

5.  The  normal  physiologic  stimulus  : 

(a)   Centrifugal  or  efferent,  if  proceeding  from  the  center  toward  the 

periphery. 
(6)   Centripetal  or  afferent,  if  in  the  reverse  direction. 
Special  stimuli  : 

1.  Light  or  ethereal  vibrations  acting  upon  the  end  organs  of  the  optic 
nerve  in  the  retina. 

2.  Sound  or  atmospheric  undulations  acting  upon  the  end  organs  of  the 
auditory  nerve. 

3.  Heat  or  vibrations  of  the  air  upon  the  end  organs  in  the  skin. 

4.  Chemic  agencies  acting  upon  the  end  organs  of  the  olfactory  and  gus- 
tatory nerves. 

Nature  of  the  Nerve  Impulse. — As  to  the  nature  of  the  nerve  im- 
pulse generated  by  any  of  the  foregoing  stimuli  either  general  or  special, 
but  little  is  known.  It  has  been  supposed  to  partake  of  the  nature  of  a 
molecular  disturbance,  a  combination  of  physical  and  chemical  processes 
attended  by  the  liberation  of  energy,  which  propagates  itself  from  molecule 
to  molecule.  Judging  from  the  deflections  of  the  galvanometer  needle  it  is 
probable  that  when  the  nerve  impulse  makes  its  appearance  at  any  given 
point  it  is  at  first  feeble  but  soon  reaches  a  maximum  development  after 
which  it  speedily  declines  and  disappears.  It  may,  therefore,  be  graph- 
ically represented  as  a  wave-like  movement  with  a  definite  length  and  time 
duration.  Under  strictly  physiological  conditions  the  nerve  impulse  passes 
in  one  direction  only  ;  in  efferent  nerves  from  the  center  to  the  periphery, 
in  afferent  nerves  from  the  periphery  to  the  center.  Experimentally,  how 
ever,  it  can  be  demonstrated  that  when  a  nerve  impulse  is  aroused  in  the 
course  of  a  nerve  by  an  adequate  stimulus  it  travels  equally  well  in  both 
directions  from  the  point  of  stimulation.  When  once  started  the  impulse 
is  confined  to  the  single  fiber  and  does  not  diffuse  itself  to  fibers  adjacent 
to  it  in  the  same  nerve  trunk. 

Rapidity  of  Transmission  of  Nerve  Force. — The  passage  of  a  ner- 
vous impulse,  either  from  the  brain  to  the  periphery  or  in  the  reverse  direc- 
tion, requires  an  appreciable  period  of  time.  The  velocity  with  which  the 
impulse  travels  in  human  sensory  nerves  has  been  estimated  at  about  190 
feet  a  second,  and  for  motor  nerves  at  from  1 00  to  200  feet  a  second. 
The  rate  of  movement  is,  however,  somewhat  modified  by  temperature, 
cold  lessening  and  heat  increasing  the  rapidity  ;  it  is  also  modified  by  elec- 
tric conditions,  by  the  action  of  drugs,  the  strength  of  the  stimulus,  etc. 
The  rate  of  transmission  through  the  spinal  cord  is  considerably  slower 


PHYSIOLOGY    OF   NERVE   TISSUE.  85 

than  in  nerves,  the  average  velocity  for  voluntary  motor  impulses  being 
only  33  feet  a  second,  for  sensitive  impressions  40  feet,  and  for  tactile 
impressions  140  feet  a  second. 

Electric  Currents  in  Muscles  and  Nerves. — If  a  muscle  or  nerve 
be  divided  and  non-polarizable  electrodes  be  placed  upon  the  natural  longi- 
tudinal surface  at  the  equator,  and  upon  the  transverse  section,  electric 
currents  are  observed  with  the  aid  of  a  delicate  galvanometer.  The  direc- 
tion of  the  current  is  always  from  the  positive  equatorial  surface  to  the 
negative  transverse  surface.  The  strength  of  the  current  increases  or  di- 
minishes according  as  the  positive  electrode  is  moved  toward  or  from  the 
equator.  When  the  electrodes  are  placed  on  the  two  transverse  ends  of  a 
nerve,  an  axial  current  will  be  observed  the  direction  of  which  is  opposite  to 
that  of  the  normal  impulse  of  the  nerve. 

The  electromotive  force  of  the  strongest  nerve-current  has  been  estimated 
to  be  equal  to  the  0.026  of  a  Daniell  battery ;  the  force  of  the  current  of 
the  frog  muscle,  about  0.05  to  0.08  of  a  Daniell.  *- 

Negative  Variation  of  Currents  in  Muscles  and  Nerves. — If  a 
muscle  or  nerve  be  thrown  into  a  condition  of  tetanus,  it  will  be  observed 
that  the  currents  undergo  a  diminution  or  negative  variation,  a  change 
which  passes  along  the  nerve  in  the  form  of  a  wave  and  with  a  velocity 
equal  to  the  rate  of  transmission  of  the  nerve  impulse.  The  wave-length 
of  a  single  negative  variation  has  been  estimated  to  be  eighteen  millimeters, 
the  period  of  its  duration  being  from  0.0005  to  0.0008  of  a  second. 

It  is  asserted  by  Hermann  that  perfectly  fresh,  uninjured  muscles  and 
nerves  are  devoid  of  currents,  and  that  the  currents  observed  are  the 
result  of  molecular  death  at  the  point  of  section,  this  point  becoming 
negative  to  the  equatorial  point.  He  applies  the  term  "  action  currents  " 
to  the  currents  obtained  when  a  muscle  is  thrown  into  a  state  of  activity. 

Electric  Properties  of  Nerves. — When  a  galvanic  current  is  made  to 
flow  along  a  motor  nerve  from  the  center  to  the  periphery,  from  the  posi- 
tive to  the  negative  pole,  it  is  known  as  the  direct,  descending,  or  centrif- 
ugal current.  When  it  is  made  to  flow  in  the  reverse  direction,  it  is  known 
as  the  inverse,  ascending,  or  centripetal  current. 

The  passage  of  a  direct  current  enfeebles  the  excitability  of  a  nerve  ; 
the  passage  of  the  inverse  current  increases  it.  The  excitability  of  a  nerve 
may  be  exhausted  by  the  repeated  applications  of  electricity ;  when  thus 
exhausted,  it  may  be  restored  by  repose,  or  by  the  passage  of  the  inverse 
current  if  the  nerve  has  been  exhausted  by  the  direct  current,  or  vice  versa.      / 


86  HUMAN   PHYSIOLOGY. 

During  the  actual  passage  of  a  feeble  constant  current,  in  either  direction, 
neither  pain  nor  muscular  contraction  is  ordinarily  manifested ;  if  the 
current  be  very  intense,  the  nerve  may  be  disorganized  and  its  excitability 
destroyed. 

Electrotonus. — The  passage  of  a  direct  galvanic  current  through  a  por- 
tion of  a  nerve  excites  in  the  parts  beyond  the  electrodes  a  condition  of 
electric  tension,  or  electrotonus ,  during  which  the  excitability  of  the  nerve 
is  decreased  near  the  anode  or  positive  pole,  and  increased  near  the  cathode 
or  negative  pole ;  the  increase  of  excitability  in  the  catelectrotonic  area — 
that  nearest  the  muscle — being  manifested  by  a  more  marked  contraction  of 
the  muscle  than  the  normal  when  the  nerve  is  irritated  in  this  region.  The 
passage  of  an  inverse  galvanic  current  excites  the  same  condition  of  elec- 
trotonus ;  the  diminution  of  excitability  near  the  anode,  the  anelec- 
trotonic  area, — that  now  nearest  the  muscle, — being  manifested  by  a  less 
marked  contraction  than  the  normal  when  the  nerve  is  stimulated  in  this 
region.  Between  the  electrodes  is  a  neutral  point,  where  the  catelectrotonic 
area  emerges  into  the  anelectrotonic  area.  If  the  current  be  a  strong  one, 
the  neutral  point  approaches  the  cathode  ;  if  weak,  it  approaches  the  anode. 

When  a  nervous  impulse  passes  along  a  nerve,  the  only  appreciable  effect 
is  a  change  in  its  electric  condition,  there  being  no  change  in  its  tempera- 
ture, chemic  composition,  or  physical  condition.  The  natural  nerve- cur- 
rents, which  are  always  present  in  a  living  nerve  as  a  result  of  its  nutritive 
activity,  in  great  part  disappear  during  the  passage  of  an  impulse,  under- 
going a  negative  variation. 

Law  of  Contraction. — If  a  feeble  galvanic  current  be  applied  to  a 
recent  and  excitable  nerve,  contraction  is  produced  in  the  muscles  only 
upon  the  making  of  the  circuit  with  both  the  direct  and  inverse  currents. 

If  the  current  be  moderate  in  intensity,  the  contraction  is  produced  in 
the  muscle,  both  upon  the  making  and  breaking  of  the  circuit,  with  both 
the  direct  and  inverse  currents. 

If  the  current  be  inte?ise,  contraction  is  produced  only  when  the  circuit 
is  made  with  the  direct  current,  and  only  when  it  is  broken  with  the  inverse 
current. 

FOODS  AND  DIETETICS. 

During  the  functional  activity  of  every  organ  and  tissue  of  the  body  the 
living  material  of  which  it  is  composed — the  protoplasm — undergoes  more 
or  less  disintegration.  Through  a  series  of  descending  chemic  stages  it  is 
reduced  to  a  number  of  simpler  compounds,  which  are  of  no  further  value 
to  the  body,  and  which  are  in  consequence  eliminated  by  the  various  elim- 


FOODS    AND    DIETETICS.  87 

inating  or  excretory  organs — the  lungs,  kidneys,  skin,  liver.  Among  these 
compounds  the  more  important  are  carbon  dioxid,  urea,  and  uric  acid. 
Many  other  compounds,  inorganic  as  well  as  organic,  are  also  eliminated 
in  the  water  discharged  from  the  body,  in  which  they  are  held  in  solution. 
Coincident  with  this  disintegration  of  the  tissues  there  is  an  evolution  or 
disengagement  of  energy,  particularly  in  the  form  of  heat. 

In  order  that  the  tissues  may  regain  their  normal  composition  and  thus 
be  enabled  to  continue  in  the  performance  of  their  functions,  they  must  be 
supplied  with  the  same  nutritive  materials  of  which  their  protoplasm  orig- 
inally consisted — viz.,  water,  inorganic  salts,  proteids,  sugar,  fat.  These 
materials  are  furnished  by  the  blood  during  its  passage  through  the  capillary 
blood-vessels.  The  blood  is  a  reservoir  of  nutritive  material  in  a  condition 
to  be  absorbed,  organized,  and  transformed  into  new  living  tissue. 

Inasmuch  as  the  loss  of  material  from  the  body  daily,  which  is  very 
great,  is  compensated  for  under  other  forms  by  the  blood,  it  is  evident  that 
this  fluid  would  rapidly  diminish  in  volume  were  it  not  restored  by  the  intro- 
duction of  new  and  corresponding  materials.  As  soon  as  the  blood  vol- 
ume falls  to  a  certain  point,  the  sensations  of  hunger  and  thirst  arise, 
which  in  a  short  time  lead  to  the  necessity  of  taking  food. 

In  addition  to  the  direct  appropriation  of  food  by  the  tissues  it  is  highly 
probable  that  an  indefinite  amount  undergoes  oxidation  and  disintegration 
without  ever  becoming  an  integral  part  of  the  tissues,  and  thus  directly 
contributes  to  the  production  of  heat. 

Inanition  or  Starvation. —  If  these  nutritive  principles  be  not  supplied 
in  sufficient  quantity,  or  if  they  are  withheld  entirely,  a  condition  of  physio- 
logic decay  is  established,  to  which  the  term  inanition  or  starvation  is 
applied.  The  phenomena  which  characterizes  this  pathologic  process  are 
as  follows  —  viz.,  hunger,  intense  thirst,  gastric  and  intestinal  uneasiness 
and  pain,  muscle  weakness  and  emaciation,  a  diminution  in  the  quantity 
of  carbon  dioxid  exhaled,  a  lessening  in  the  amount  of  urine  and  its  con- 
stituents excreted,  a  diminution  in  the  volume  of  the  blood,  an  exhalation 
of  a  fetid  odor  from  the  body,  vertigo,  stupor,  delirium,  and  at  times  con- 
vulsions, a  fall  of  bodily  temperature,  and,  finally,  death  from  exhaustion. 

During  starvation  the  loss  of  different  tissues,  before  death  occurs,  aver- 
ages T^,  or  40  per  cent.,  of  their  weight. 

Those  tissues  which  lose  more  than  40  per  cent,  are  :  Fat,  93.3  ;  blood, 
75  ;  spleen,  71.4;  pancreas,  64.1  ;  liver,  52;  heart,  44.8;  intestines, 
42.4  ;  muscle,  42.3.  Those  which  lose  less  than  40 per  cent,  are  :  The 
muscular  coat  of  the  stomach,  39.7  ;  pharynx  and  esophagus,  34.2  ;  skin, 
33.3  ;  kidneys,  31. 9;  respiratory  apparatus,  22.2  ;  bones,  16.7  ;  eyes,  IO  ; 
nervous  system,  1.9. 

The  fat  entirely  disappears,  with  the  exception  of  a  small  quantity  which 


88  HUMAN   PHYSIOLOGY. 

remains  in  the  posterior  portion  of  the  orbits  and  arountl  the  kidneys. 
The  blood  diminishes  in  volume  and  loses  its  nutritive  properties.  The 
7nuscles  undergo  a  marked  diminution  in  volume  and  become  soft  and 
flabby.  The  nervous  system  is  last  to  suffer,  not  more  than  two  per  cent, 
disappearing  before  death  occurs. 

The  appearances  presented  by  the  body  after  death  from  starvation  are 
those  of  anemia  and  great  emaciation  ;  almost  total  absence  of  fat ;  blood- 
lessness ;  a  diminution  in  the  volume  of  the  organs  ;  an  empty  condition 
of  the  stomach  and  bowels,  the  coats  of  which  are  thin  and  transparent. 
There  is  a  marked  disposition  of  the  body  to  .undergo  decomposition, 
giving  rise  to  a  very  fetid  odor. 

The  duration  of  life  after  a  complete  deprivation  of  food  varies  from  eight 
to  thirteen  days,  though  life  can  be  maintained  much  longer  if  a  quantity  of 
water  be  obtained.  The  water  is  more  essential  under  these  circumstances 
than  the  solid  matters,  which  can  be  supplied  by  the  organism  itself. 

The  different  alimentary  or  nutritive  principles  which  are  appropriated 
by  the  tissues,  and  which  are  contained  within  the  various  articles  of  food, 
belong  to  both  the  organic  and  inorganic  groups  and  chemic  compounds, 
and  may  be  classified  according  to  their  composition  as  follows  : 

CLASSIFICATION    OF  ALIMENTARY    PRINCIPLES. 
i.  Proteid  Group. — Nitrogenized,  C,  O,  H,  N,  S,  P. 

Principle.  Where  Found. 

Myosin, Flesh  of  animals. 

Vitellin,  albumin,  .  Yolk  of  egg,  white  of  egg. 

Fibrin,  globulin* .  Blood  contained  in  meat. 

7   &  7        ■        "        "  ■        ■  ^ 

Casein, Mdk,  cheese. 

Gluten, ...  Grain  of  wheat  and  other  cereals. 

Vegetable  albumin, Soft,  growing  vegetables. 

Legumin, Peas,  beans,  lentils,  etc. 

Gelatin, Bones. 

2.  Oleaginous  Group. —  C,  O,  H. 

Animal  fats  and  oils, )  Found  in  the  adipose  tissue  of  ani- 

Stearin,  olein,                 .        .    .    .    >  mals,  seeds,  grains,  nuts,  fruits, 

Paltnitin,  fatty  acids, j  and  other  vegetable  tissues. 

3.  Carbohydrate  Group. —  C,  O,  H. 
Saccharose,  or  cane-sugar,    ....  Sugar-cane. 

Dextrose,  ox  glucose, \  Fruits> 

Levulose,  or  fruit-sugar,  ....   J 

Lactose,  or  milk-sugar, Milk. 

Maltose, Malt,  malt  foods. 

Starch, Cereals,  tuberous   roots,   and  legu- 
minous plants. 
Glycogen, Liver,  muscles. 


FOODS   AND   DIETETICS.  89 

4.  Inorganic  Group. —  Water;  sodium  and  potassium  chlorids  ;  sodium 
calcium,  magnesium,  and  potassium    phosphates  ;    calcium   carbonate  ; 
and  iron. 

5.  Vegetable  Acid  Group. —  Malic,   citric,    tartaric,    and   other  acids, 
found  principally  in  fruits. 

6.  Accessory  Foods. —  Tea,  coffee,  alcohol,  cocoa,  etc. 

The  proteid  principlts  of  the  food,  after  undergoing  digestion  and  con- 
version into  peptones,  are  absorbed  and  transformed  into  the  form  of  pro- 
teids  characteristic  of  the  blood  plasma  and  the  lymph.  Of  the  proteids 
thus  brought  into  relation  with  the  living  protoplasm,  a  small  percentage 
only  is  utilized  in  the  repair  of  its  substance.  This  is  known  as  tissue  pro- 
teid. A  large  percentage  circulating  among  and  permeating  the  tissues  is 
acted  upon  by  them  directly,  and  reduced  to  simpler  compounds  without 
ever  becoming  a  part  of  the  tissue  itself.  This  is  known  as  circulating 
proteid.  In  the  process  of  tissue  metabolism  all  the  proteids  suffer  disin- 
tegration, and  give  rise  to  the  production  of  some  carbon-holding  com- 
pound, probably  fat,  and  some  nitrogen-holding  compounds  which  event- 
ually produce  urea.  The  intermediate  stages  are  possibly  represented  by 
glycin,  creatin,  uric  acid,  etc.  An  excess  of  proteids  in  the  food  is  followed 
by  their  decomposition,  by  the  pancreatic  juice,  into  leucin  and  tyrosin, 
which,  by  the  agency  of  the  liver,  are  converted  into  urea.  The  disinte- 
gration of  the  proteids  is  attended  by  the  disengagement  of  heat :  they  thus 
contribute  to  the  energy  of  the  body. 

The  oleaginous  principles,  after  digestion,  are  absorbed  into  the  blood, 
from  which  they  rapidly  disappear.  It  is  probable  that  a  portion  of  the 
fat  enters  directly  into  the  composition  of  living  protoplasm,  out  of  which 
it  again  emerges  at  some  subsequent  stage  in  the  form  of  small  drops  which 
make  their  appearance  in  the  protoplasmic  cells  of  the  connective  areolar 
tissue,  thus  giving  rise  to  the  adipose  tissue.  Another  portion  probably 
undergoes  direct  oxidation. 

The  carbohydrate  principles,  after  digestion,  are  absorbed  as  dextrose 
and  temporarily  stored  up  in  the  liver  as  glycogen.  The  intermediate 
stages  which  sugar  passes  through  and  the  combinations  into  which  it 
enters  between  its  absorption  and  its  elimination  are  but  imperfectly  under- 
stood. That  it  contributes  to  the  accumulation  of  fat  is  probable,  though 
it  is  doubtful  if  it  is  ever  converted  into  fat.  A  large  percentage  of  the 
sugar  absorbed  is  at  once  oxidized.  The  reduction  of  fat  and  sugar  to 
carbon  dioxid  and  water,  under  which  forms  they  are  eliminated  from  the 
body,  is  accompanied  by  the  disengagement  of  a  large  quantity  of  heat. 
7 


90  HUMAN    PHYSIOLOGY. 

Water  is  present  in  all  the  fluids  and  solids  of  the  body.  It  promotes 
the  absorption  of  new  material  from  the  alimentary  canal ;  it  holds  the 
various  ingredients  of  the  blood,  lymph,  and  other  fluids  in  solution  ;  it 
hastens  the  absorption  of  waste  products  from  the  tissues,  and  promotes  their 
speedy  elimination  from  the  body. 

Sodiiwi  chlorid  is  present  in  all  parts  of  the  body  to  the  extent  of  no 
gm.  The  average  amount  eliminated  daily  is  15  gm.  Its  necessity  as  an 
article  of  diet  is  at  once  apparent.  Taken  as  a  condiment,  it  imparts 
sapidity  to  the  food,  excites  the  flow  of  the  digestive  fluids,  promotes  the 
absorption  and  assimilation  of  the  albumins,  influences  the  passage  of 
nutritive  material  through  animal  membranes,  and  furnishes  the  chlorin  for 
the  free  hydrochloric  acid  of  the  gastric  juice.  In  some  unknown  way  it 
favorably  promotes  the  activity  of  the  general  nutritive  process. 

The  potassium  salts  are  also  essential  to  the  normal  activity  of  the  nutri- 
tive process.  When  deprived  of  these  salts,  animals  become  weak  and 
emaciated.  When  given  in  small  doses,  they  increase  the  force  of  the 
heart-beat,  raise  the  arterial  pressure,  and  thus  increase  the  action  of  the 
circulation  of  the  blood. 

The  calcium  phosphate  and  carbonate  are  utilized  in  imparting  solidity 
to  the  tissues,  more  especially  the  bones  and  teeth.  Many  articles  of  food 
contain  these  salts  in  quantities  sufficient  to  restore  the  amount  lost  daily. 

The  vegetable  acids  increase  the  secretions  of  the  alimentary  canal,  and 
are  apt,  in  large  amounts,  to  produce  flatulence  and  diarrhea.  After  enter- 
ing into  combination  with  bases  to  form  salts,  they  stimulate  the  action  of 
the  kidneys  and  promote  a  greater  elimination  of  all  the  urinary  constitu- 
ents. In  some  unknown  way  they  influence  nutrition  ;  when  deprived  of 
these  acids,  the  individual  becomes  scorbutic. 

The  accessory  foods,  coffee  and  tea,  when  taken  in  moderation,  overcome 
the  sense  of  fatigue  and  mental  unrest  consequent  on  excessive  physical 
and  mental  exertion.  Coffee  increases  the  action  of  the  intestinal  glands 
and  acts  as  a  laxative.  After  absorption,  its  active  principle,  caffein, 
stimulates  the- action  of  the  heart,  raises  the  arterial  pressure,  and  excites 
the  action  of  the  brain.  Tea  acts  as  an  astringent,  owing  to  the  tannic 
acid  it  contains.  One  effect  of  the  tannic  acid  is  to  coagulate  the  digestive 
ferments  and  to  interfere  with  the  activity  of  the  digestive  process. 

Alcohol,  when  introduced  into  the  system  in  small  quantities,  undergoes 
oxidation  and  contributes  to  the  production  of  force,  and  is  thus  far  a  food. 
It  excites  the  gastric  glands  to  increased  secretion,  improves  the  digestion, 
accelerates  the  action  of  the  heart,  and  stimulates  the  activities  of  the 
nerve  centers.     In  zymotic  diseases,  and  in  all  cases  of  depression  of  the 


FOODS   AND   DIETETICS.  91 

vital  powers,  it  is  most  useful  as  a  restorative  agent.  When  taken  in 
excessive  quantities,  it  is  eliminated  by  the  lungs  and  kidneys.  The  meta- 
morphosis of  the  tissue  is  retarded,  the  elimination  of  urea  and  carbonic  acid 
is  lessened,  the  temperature  is  lowered,  the  muscular  powers  are  impaired, 
and  the  resistance  to  depressing  external  influences  is  diminished.  When 
taken  throughout  a  long  period  of  time,  alcohol  impairs  digestion,  produces 
gastric  catarrh,  and  disorders  the  secreting  power  of  the  hepatic  cells.  It 
also  diminishes  the  muscular  power  and  destroys  the  structure  and  compo- 
sition of  the  cells  of  the  brain  and  spinal  cord.  The  connective  tissue  of 
the  body  increases  in  amount,  and,  subsequently  contracting,  gives  rise  to 
sclerosis. 

A  proper  combination  of  various  alimentary  principles  is  essential  for 
healthy  nutrition,  no  one  class  being  capable  of  maintaining  life  for  any 
definite  length  of  time. 

The  albuminous  food  in  excess  promotes  the  arthritic  diathesis,  mani- 
festing itself  as  gout,  gravel,  etc. 

The  oleaginous  food  in  excess  gives  rise  to  the  bilious  diathesis,  while  a 
deficiency  of  it  promotes  the  scrofulous. 

The  farinaceous  food  when  long  continued  in  excess,  favors  the  rheu- 
matic diathesis  by  the  development  of  lactic  acid. 

The  quantities  of  the  different  nutritive  materials  which  are  required 
daily  for  the  growth  and  repair  of  the  tissues  and  for  the  evolution  of  heat 
have  been  variously  estimated  by  different  observers.  The  following  table 
shows  the  average  diet  scale  of  Vierordt,  and  the  amount  of  waste  products 
to  which  it  would  give  rise  : 

Comparison  of  the  Ingesta  and  Egesta. 

Ingest  a.  Egesta. 

Proteids,    ....       1 20  grams.  Urea,     ....        40  grams. 

Fat, 90  "  Inorganic  salts,        32  " 

Starch,   .    .        .    .      330  "  Feces,    ....      104  " 

Inorganic  salts,      .        32  "  Carbon  dioxid,      800  " 

Water,    .....  2,800  "  Water,  ....  3,096  " 

Oxygen,     ....      700  "                    Total,    .    .  4,072  " 

Total,     .    .    .  4,072  " 

Other  estimates  as  to  the  amount  of  the  organic  substances  required 
daily  are  as  follows  : 


Ranke. 

Voit. 

Moleschott. 

Proteid,    .    .100 

118 

130  grams. 

Fat,       ...  100 

50 

84      " 

Starch,      .   .  240 

500 

404      " 

92  HUMAN    PHYSIOLOGY. 

The  Energy  of  the  Animal  Body.  —  The  food  consumed  daily  not 
only  repairs  the  loss  of  material  from  the  body,  but  also  furnishes  the 
energy  to  replace  that  which  is  expended  daily  in  the  shape  of  heat  and 
motion.  All  the  energy  of  the  body  can  be  traced  to  the  chemic  changes 
going  on  in  the  tissues,  and  more  particularly  to  those  changes  involved  in 
the  oxidation  of  the  foods. 

The  amount  of  heat  yielded  by  any  given  food  principle  can  be  deter- 
mined by  burning  it  to  carbon  dioxid  and  water,  and  ascertaining  the 
extent  to  which  it  will,  when  so  liberated,  raise  the  temperature  of  a  given 
volume  of  water.  This  amount  of  heat  may  be  expressed  in  gram  degrees 
of  heat  —  i.  e. ,  calories  or  kilogrammeters  of  work.  A  calorie  is  the  amount 
of  heat  required  to  raise  the  temperature  of  one  gram  of  water  one  degree 
Centigrade,  or  one  kilograiti  of  water  one  degree  Centigrade.  A  kilogram- 
meter  of  work  is  the  amount  of  heat  energy  required  to  raise  a  weight  of 
one  kilogram  a  distance  of  one  meter. 

The  following  estimates  give,  approximately,  the  number  of  calories  pro- 
duced when  the  food  is  reduced  within  the  body  to  urea,  carbon  dioxid, 
and  water  : 

I  gram  of  proteid  yields  4,124  kilogram  calories. 
I        "        fat  "      9,353        "  " 

1        "        starch        "      4,116        "  " 

The  total  number  of  kilogram  calories  yielded  by  any  given  diet  scale 
can  be  readily  determined  by  multiplying  the  preceding  factors  by  the 
quantities  of  material  consumed.  The  diet  scale  of  Ranke,  for  example, 
yields  the  following  amount : 

100  grams  of  proteid  yield  412.4  calories. 
100         "        fat  "    935.3         " 

240         "        starch        "    987.8         " 

Total, 2,335.5         " 

It  has  also  been  determined  experimentally  that  one  gram  of  proteid,  one 
gram  of  fat,  and  one  gram  of  starch,  when  completely  oxidized,  will  yield 
energy  sufficient  to  perform  1,850,  3,841,  and  1,567  kilogrammeters  of 
work,  respectively. 

The  total  energy  of  the  Ranke  diet  scale  can  be  easily  calculated  —  e.  g.  : 

100  grams  of  proteid  yield  185,000  kilogrammeters. 
100         "        fat  "    384,100  " 

240         "        starch         "    397,680  " 

Total,    ....  9667780  " 


FOODS    AND   DIETETICS.  93 

It  will  be  thus  seen  that  the  food  consumed  daily  yields  2,335,000  gmm 
calories,  or  2,335  kilogram  calories,  which  can  be  translated  into  its  me- 
chanical equivalent,  966,780  kilogrammeters  of  work. 

The  amount  of  food  required  in  twenty-four  hours  is  estimated  from 
the  total  quantity  of  carbon  and  nitrogen  excreted  from  the  body  in 
twenty -four  hours,  these  two  elements  representing  the  waste  or  destruction 
of  the  carbonaceous  and  nitrogenized  compounds.  It  has  been  determined 
by  experimentation  that  about  4,600  grains  of  carbon  and  about  300  grains 
of  nitrogen  are  eliminated  from  the  body  daily,  the  ratio  being  about  15 
to  I.  That  the  body  may  be  kept  in  its  normal  condition,  a  proper  pro- 
portion of  carbonaceous  (bread)  to  nitrogenized  (meat)  food  should  be  ob- 
served in  the  diet. 

The  method  of  determining  the  proper  amounts  of  both  kinds  of  food  is 
as  follows  : 

1,000  grs.  of  bread  (2  oz. )  contain  300  grs.  C  and  10  grs.  N. 

To  obtain  the  requisite  amount  of  nitrogen  from  bread,  30,000  grains,  or 
about  four  pounds,  containing  9,000  grains  of  carbon  and  300  of  nitrogen, 
would  have  to  be  consumed.  On  such  a  diet  there  would  be  a  large 
excess  of  carbon,  which  would  be  undesirable.  On  a  meat  diet  the  reverse 
obtains  : 

1,000  grs.  of  meat  (2  oz. )  contain  100  grs.  C  and  30  grs.  N. 

To  obtain  the  requisite  amount  of  carbon  from  meat,  45,000  grains,  or 
about  6*4  pounds,  containing  4,500  grains  of  carbon  and  1,350  grains  of 
nitrogen  would  have  to  be  consumed.  Under  such  circumstances  there 
would  arise  an  excess  of  nitrogen  in  the  system,  which  would  be  equally 
undesirable  and  injurious.  By  combining  these  two  articles,  however,  in 
proper  proportion,  the  requisite  amounts  of  carbon  and  nitrogen  can  be  ob- 
tained without  any  excess  of  either — e.  g.  : 

2  pounds  of  bread  contain  4,630  grs.  C  and   154  grs.  N. 
%        "  meat        "  463    "     "     "     154  "     " 

5,093  C.  308  N. 

The  amount  of  carbon  and  nitrogen  necessary  to  compensate  for  the  loss 
to  the  system  daily  would  be  contained  in  the  foregoing  amount  of  food. 
As  about  3^  ounces  of  oil  or  butter  are.  consumed  daily,  the  quantity  of 
bread  can  be  reduced  to  19  ounces.  In  the  quantities  of  bread  and  meat 
just  mentioned  there  are  4.2  ounces  albumin,  9.3  sugar  and  starch. 


94 


HUMAN   PHYSIOLOGY. 


The  alimentary  principles  are  not  introduced  into  the  body  as  such, 
but  are  combined  in  proper  proportions  to  form  compound  substances, 
termed  foods, — e.  g.,  bread,  milk,  eggs,  meat,  etc., — the  nutritive  value  of 
each  depending  upon  the  extent  to  which  these  principles  exist. 

The  following  tables  show  the  average  composition  of  various  articles 
of  food  : 

COMPOSITION   OF  ANIMAL   FOODS. 


In  ioo  Parts. 

Beef. 

Veal. 

Mutton. 

Pork. 

Fowl. 

Fish. 

Water,     .... 

76.25 

77.82 

75-59 

72.57 

70.80 

79-30 

Proteid,   .... 

20.24 

I9.86 

17. 11 

19-31 

22.70 

18.30 

Fat, 

1.68 

O.82 

5-47 

5.82 

4.IO 

O.70 

Carbohydrates, 

0.50 

O.80 

0.60 

O  60 

I.20 

O.90 

1-38 

O.70 

1  23 

I.70 

I.20 

o.So 

COMPOSITION    OF  VEGETABLE  FOODS. 


In  ioo  Parts. 

Beans. 

Peas. 

Pota- 
toes 

Turnips. 

Cabbage. 

Aspara- 
gus. 

Water,     .... 

13-74 

14.99 

75-47 

89.42 

89.97 

93-75 

Proteid,  .... 

23.21 

22.85 

1-95 

1-35 

I.89 

1.79 

Fat, 

2.14 

I.79 

0.15 

O.18 

0.20 

0.25 

Carbohydrates, 

53-67 

52-36 

20.69 

7.36 

4.87 

2.63 

Cellulose,    . 

3- 69 

5-43 

0.76 

O.94 

.  I.84 

1.04 

Salts,    ... 

3-55 

2.58 

0.98 

0.75 

I.23 

o.54 

DIGESTION. 

ICOMPOSITION  OF  CEREAL  FOODS. 


95 


In  ioo  Parts. 

Whf.at. 

Rye. 

12.65 

Barley. 

13-77 

Oats. 
12.37 

Corn. 
I3.IO 

Rice. 

Water,     .         .    . 

I3-56 

13.12 

Proteid,           .    . 

12.35 

12-55 

11. 14 

IO.4I 

9.85 

7.88 

Fat, 

i-75 

I.97 

2.16 

5-23 

4-57 

O.85 

Carbohydrates. 

67.90 

67.95 

64-93 

57-78 

68.42 

76.55 

Cellulose,     .    .    . 

2.63 

3.00 

5-3i 

1 1 . 1 9 

2.50 

0.55 

Salts, 

1. 81 

1.88 

2.69 

3.02 

1.56 

I.05 

DIGESTION. 

Digestion  is  a  physical  and  chemic  process  by  which  the  food  intro- 
duced into  the  alimentary  canal  is  liquefied  and  its  nutritive  principles  are 
transformed  by  the  digestive  fluids  into  new  substances  capable  of  being 
absorbed  into  the  blood. 

The  digestive  apparatus  consists  of  the  alimentary  canal  and  its 
appendages — viz. ,  teeth  ;  salivary,  gastric,  and  intestinal  glands  ;  liver  ;  and 
pancreas. 

Digestion  maybe  divided  into  seven  stages:  prehension,  mastication, 
insalivation,  deglutition,  gastric  and  intestinal  digestion,  and  defecation. 

Prehension,  the  act  of  conveying  food  into  the  mouth,  is  accomplished 
by  the  hands,  lips,  and  teeth. 

MASTICATION. 

Mastication  is  the  trituration  of  the  food,  and  is  accomplished  by  the 

teeth  and  lower  jaw  under  the  influence  of  muscular  contraction.     When 

thoroughly  divided,   the    food  presents   a  larger   surface    for   the  solvent 

action  of  the  digestive  fluids,  thus  aiding  the  general  process  of  digestion. 

The  teeth  are  thirty -two  in  number,  sixteen  in  each  jaw,  and  divided 
into  four  incisors  or  cutting   teeth,  two  canines,   four  bicuspids,  and   six 


96  HUMAN    PHYSIOLOGY. 

molars  or  grinding  teeth  ;  each  tooth  consists  of  a  crown  covered  by 
enamel,  a  neck,  and  a  root  surrounded  by  the  crusta  petrosa  and  embedded 
in  the  alveolar  process  ;  a  section  through  a  tooth  shows  that  its  substance 
is  made  of  dentine,  in  the  center  of  which  is  the  pulp  cavity  containing 
blood-vessels  and  nerves. 

The  lower  Jaw  is  capable  of  making  a  downward  and  an  upward,  a 
lateral  and  an  anteroposterior  movement,  dependent  upon  the  construction 
of  the  temporomaxillary  articulation. 

The  jaw  is  depressed  by  the  contraction  of  the  digastric ',  geniohyoid,  mylo- 
hyoid, and  platysma  myoides  muscles;  elevated  by  the  temporal,  masseter, 
and  internal  pterygoid  muscles ;  moved  laterally  by  the  alternate  contrac- 
tion of  the  external  pterygoid  muscles  ;  moved  anteriorly  by  the  pterygoid, 
and  posteriorly  by  the  united  actions  of  the  geniohyoid,  mylohyoid,  and 
posterior  fibers  of  the  temporal  muscles. 

The  food  is  kept  between  the  teeth  by  the  intrinsic  and  extrinsic  muscles 
of  the  tongue  from  within,  and  the  orbicularis  oris  and  buccinator  muscles 
from  without. 

The  movements  of  mastication,  though  originating  in  an  effort  of 
the  will  and  under  its  control,  are,  for  the  most  part,  of  an  automatic  or 
reflex  character,  taking  place  through  the  medulla  oblongata  and  induced 
by  the  presence  of  food  within  ihe  mouth.  The  nerves  and  nerve- centers 
involved  in  this  mechanism  are  shown  in  the  following  table  : 

NERVOUS  CIRCLE  OF  MASTICATION. 

Afferent  or  Excitor  Nerves.  Efferent  or  Motor  Nerves. 

1.  Lingual  branch  of  5th  pair.  1.   3d  branch  of  5th  pair. 

2.  Glossopharyngeal.  2.    Hypoglossal. 

3.   Facial. 

The  impressions  made  upon  the  terminal  filaments  of  the  sensory  nerves 
are  transmitted  to  the  medulla  ;  motor  impulses  are  here  generated  which 
are  transmitted  through  motor  nerves  to  the  muscles  involved  in  the  move- 
ments of  the  lower  jaw.  The  medulla  not  only  generates  motor  impulses, 
but  coordinates  them  in  such  a  manner  that  the  movements  of  mastication 
may  be  directed  toward  the  accomplishment  of  a  definite  purpose. 

INSALIVATION. 

Insalivation  is  the  incorporation  of  the  food  with  the  saliva  secreted 
by  the  parotid,  submaxillary,  and  sublingual  glands ;  the  parotid  saliva, 
thin  and  watery,  is  poured  into  the  mouth  through  Steno's  duct ;  the  sub- 


DIGESTION. 


97 


maxillary  and  sublingual  salivas,  thick  and  viscid,  are  poured  into  the 
mouth  through  Wharton's  and  Bartholin's  ducts. 

In  their  minute  structure  the  salivary  glands  resemble  one  another.  They 
belong  to  the  racemose  variety,  and  consist  of  small  sacs  or  vesicles,  which 
are  the  terminal  expansions  of  the  smallest  salivary  ducts.  Each  vesicle  or 
acinus  consists  of  a  basement  membrane  surrounded  by  blood-vessels  and 
lined  with  epithelial  cells.  In  the  parotid  gland  the  lining  cells  are 
granular  and  nucleated ;  in  the  submaxillary  and  sublingual  glands  the 
cells  are  large,  clear,  and  contain  a  quantity  of  mucigen.  During  and 
after  secretion  very  remarkeble  changes  take  place  in  the  cells  lining  the 
acini,  which  are  in  some  way  connected  with  the  essential  constituents 
of  the  salivary  fluids. 

In  a  living  serous  gland, — e.  g.,  parotid, — during  rest,  the  secretory  cells 
lining  the  acini  of  the  gland  are  seen  to  be  filled  with  fine  granules,  which 
are  often  so  abundant  as  to  obscure  the  nucleus  and  enlarge  the  cells  until 
the  lumen  of  the  acinus  is  almost  obliterated.  (See  P'ig.  II.)  When  the 
gland  begins  to  secrete  the  saliva,  the  granules  disappear  from  the  outer 


Fig.  ii.— Cells   of  the  Alveoli   of  a  Serous   or  Watery  Salivary  Gland. — 
(  Yeo's  "  Text-Book  of  Physiology.") 

A.  After  rest.     B.    After  a  short  period  of  activity.     C.    After  a  prolonged  period  of 

activity. 

boundary  of  the  cells,  which  then  become  clear  and  distinct.  At  the  end 
of  the  secretory  activity  the  cells  have  been  freed  of  granules  and  have 
become  smaller  and  more  distinct  in  outline.  It  would  seem  that  the 
granular  matter  is  formed  in  the  cells  during  the  period  of  rest  and  dis- 
charged into  the  ducts  during  the  activity  of  the  gland. 

In  the  mucous  glands — e.  g.,  submaxillary  and  sublingual — the  changes 
that  occur  in  the  cells  are  somewhat  different.  (See  Fig.  12.)  During 
the  intervals  of  digestion  the  cells  lining  the  gland  are  large,  clear,  and 
highly  refractive,  and  contain  a  large  quantity  of  mucigen.  After  secretion 
has  taken  place  the  cells  exhibit  a  marked  change.  The  mucigen  cells 
have  disappeared,  and  in  their  place  are  cells  which  are  small,  dark,  and 


98 


HUMAN   PHYSIOLOGY. 


Fig.  12. — Section  of  a  Mucous  Gland. — (Lavdowsky.) 
A.  In  a  state  rest.     B.  After  it  has  been  for  some  time  actively  secreting. 

composed  of  protoplasm.  It  would  appear  that  the  cells,  during  rest, 
elaborate  the  mucigen,  which  is  discharged  into  the  tubules  during  secretory 
activity,  to  become  part  of  the  secretion. 

Saliva  is  an  opalescent,  slightly  viscid,  alkaline  fluid,  having  a  specific 
gravity  of  1. 005.  Microscopic  examination  reveals  the  pfesence  of 
salivary  corpuscles  and  epithelial  cells.  Chemically  it  is  composed  of 
water,  proteid  matter,  a  ferment  (ptyalin),  and  inorganic  salts.  The 
amount  secreted  in  twenty-four  hours  is  about  2.l/2  lbs.  Its  function  is 
twofold  : 

1.  Physical. — Softens  and  moistens  the  food,  agglutinates  it,  and  facili- 
tates swallowing. 

2.  Chemic. — Converts  starch  into  sugar.  This  action  is  due  to  the  pres- 
ence of  the  organic  ferment,  ptyalin.  Ptyalin  is  an  amorphous  nitrog- 
enized  substance,  which  can  be  precipitated  from  the  saliva  by  calcium 
phosphate.  Its  power  of  converting  starch  into  sugar  is  manifested  most 
decidedly  at  the  temperature  of  the  living  body  and  in  a  slightly  alkaline 
medium.  The  conversion  of  starch  into  sugar  takes  place  through 
several  stages,  the  nature  of  which  depends  upon  the  structure  of  the 
starch  granule.  This  consists  of  two  portions,  a  stroma  of  cellulose  and 
a  contained  material,  granulose,  which  is  the  more  abundant  and  impor- 
tant of  the  two.  When  subjected  to  the  action  of  boiling  water,  the 
starch  granule  swells  up  and  bursts,  forming  a  viscid,  opalescent  mass 
of  starch  paste.  If  saliva  be  now  added  to  this  paste  and  kept  at  a 
temperature  of  IO40  F.  for  a  few  minutes,  the  paste  becomes  clear  and 
limpid.     The  first  stage   in  the  digestion  is  now   complete,   with  the 


DIGESTION.  99 

formation  of  soluble  starch.  If  the  action  of  saliva  be  continued,  a 
number  of  substances  intermediate  between  starch  and  sugar  are  formed, 
to  which  the  name  dextrin  has  been  given.  Among  these  may  be 
mentioned  : 

a.  Erythrodextrin,  which  gives  the  reddish-brown  color  with  iodin. 
As  the  digestion  continues  and  sugar  is  formed,  the  erythrodextrin 
disappears,  giving  way  to — 

b.  Achroodextrin,  which  yields  no  coloration  with  iodin,  but  which  may 
be  precipitated  by  alcohol. 

The  sugar  formed  by  the  action  of  saliva  is  maltose,  the  formula  for 
which  is  C12H22On.     A  small  quantity  of  dextrose  is  also  formed. 

NERVOUS  CIRCULATION   OF   INSALIVATION. 

Afferent  or  Excitor  Nerves.  Efferent  or  Secretory  Nerves. 

1.  Lingual  branch  of  5th  pair.  I.  Auriculotemporal  branch  of  5th 

2.  Glossopharyngeal.  pair,  for  parotid  gland. 

2.   Chorda  tympani,  for  submaxil- 
lary and  sublingual  glands. 

The  centers  regulating  the  secretion  are  two — viz.,  the  medulla  oblon- 
gata and  the  submaxillary  ganglion  of  the  sympathetic,  the  latter  acting 
antagonistically  to  the  former.  Impressions  excited  by  the  food  in  the 
mouth  reach  the  medulla  oblongata  through  the  afferent  nerves  ;  motor 
impulses  are  there  generated  which  pass  outward  through  the  efferent  nerves. 

Stimulation  of  the  auriculotemporal  branch  increases  the  flow  of  saliva 
from  the  parotid  gland  ;  division  arrests  it. 

Stimulation  of  the  chorda  tympani  is  followed  by  a  dilatation  of  the 
blood-vessels  of  the  submaxillary  gland,  increased  flow  of  blood  (thus 
acting  as  a  vaso-dilator  nerve),  and  an  abundant  discharge  of  a  thin  saliva ; 
division  of  the  nerve  arrests  the  secretion. 

Stimulation  of  the  cervical  sympathetic  is  followed  by  a  contraction  of 
the  blood-vessels,  diminishing  the  flow  of  blood  (thus  acting  as  a  vaso-con- 
strictor  nerve),  and  a  diminution  of  the  secretion,  which  now  becomes  thick 
and  viscid  ;  division  of  the  sympathetic  does  not,  however,  completely 
dilate  the  vessels.  There  is  evidence  of  the  existence  of  a  local  vaso- 
motor mechanism,  which  is  inhibited  by  the  chorda  tympani,  exalted  by 
the  sympathetic. 

DEGLUTITION. 

Deglutition  is  the  act  of  transferring  food  from  the  mouth  into  the 
stomach,  and  may  be  divided  into  three  stages  : 
I.  The  passage  of  the  bolus  from  the  mouth  into  the  pharynx. 


100  HUMAN   PHYSIOLOGY. 

2.  From  the  pharynx  into  the  esophagus. 

3.  From  the  esophagus  into  the  stomach. 

In  the  first  stage,  which  is  entirely  voluntary,  the  mouth  is  closed  and 
respiration  momentarily  suspended  ;  the  tongue,  placed  against  the  roof  of 
the  mouth,  arches  upward  and  backward,  and  forces  the  bolus  in  tothe  fauces. 

In  the  second  stage,  which  is  entirely  reflex,  the  palate  is  made  tense  and 
directed  upward  and  backward  by  the  levatores  palati  and  tensores  palati 
muscles ;  the  bolus  is  grasped  by  the  superior  constrictor  muscle  of  the 
pharynx  and  rapidly  forced  into  the  esophagus. 

The  food  is  prevented  from  entering  the  posterior  nares  by  the  uvula  and 
the  closure  of  the  posterior  half-arches  (the  palatopharyngeal  muscles)  ; 
from  entering  the  larynx  by  its  ascent  under  the  base  of  the  tongue  and 
the  action  of  the  epiglottis. 

In  the  third  stage  the  longitudinal  and  circular  muscle-fibers,  contract- 
ing from  above  downward,  strip  the  bolus  into  the  stomach.  ( For  Nervous 
Mechanism  of  Deglutition,  see  Medulla  Oblongata. ) 

GASTRIC   DIGESTION. 

The  Stomach. — Immediately  beyond  the  termination  of  the  esophagus 
the  alimentary  canal  expands  and  forms  a  receptacle  for  the  temporary 
retention  of  the  food.  To  this  dilatation  the  term  stomach  has  been 
applied.  This  organ  is  somewhat  pyriform  in  outline,  and  occupies  the 
upper  part  of  the  abdominal  cavity.  It  is  about  13  inches  long,  5  deep, 
and  3^  wide,  and  has  a  capacity  of  about  five  pints.  It  presents  two 
orifices,  the  cardiac  or  esophageal,  and  the  pyloric  ;  two  curvatures,  the 
lesser  and  the  greater. 

The  left  or  cardiac  end  of  the  stomach  is  enlarged,  and  forms  the  fundus  ; 
the  right  end  is  much  narrower,  and  forms  the  pylorus.  The  stomach 
possesses  three  coats  : 

1.  The  serous,  or  reflection  of  the  peritoneum. 

2.  The  muscular,  the  fibers  of  which  are  arranged  in  a  longitudinal,  a  cir- 
cular, and  an  oblique  direction.  At  the  pyloric  end  the  circular  fibers 
increase  in  number  and  form  a  thick  ring  or  band,  which  is  known  as 
the  sphincter  of  the  pylorus. 

3.  The  mucous,  which  is  somewhat  larger  than  the  muscular  coat,  and  in 
consequence  is  thrown  into  folds  or  rugre.  The  surface  of  the  mucous 
coat  is  covered  by  tall,  narrow,  columnar  epithelium. 

Gastric  Juice. — During  the  period  of  time  the  food  remains  in  the 
stomach  it  is  subjected  to  the  disintegrating  action  of  an  acid  fluid,  the 


DIGESTION.  101 

gastric  juice.  This  fluid,  secreted  from  glands  in  the  mucous  membrane,  is 
thoroughly  incorporated  with  the  food  in  consequence  of  the  contractions 
of  the  muscular  coat.  The  food  is  gradually  liquefied  and  reduced  to  a 
form  which  partly  fits  it  for  passage  into  the  small  intestine  and  for  absorp 
tion  into  the  blood.  Gastric  juice,  when  obtained  in  a  pure  state,  is  a 
clear,  colorless  fluid,  decidedly  acid  in  reaction,  with  a  specific  gravity  of 
1005.     It  is  composed  of  the  following  ingredients  : 

COMPOSITION    OF    GASTRIC   JUICE. 

Water,        .    .                 994.404 

Hydrochloric  acid,        0.200 

Organic  matter, 3-!95 

Inorganic  salts, 2.201 

1000.000 

The  water  forms  by  far  the  largest  part  of  this  fluid,  and  serves  the 
purpose  of  holding  the  other  ingredients  in  solution,  and  by  its  saturating 
power  brings  them  into  relation  with  the  constituents  of  the  food.  Of  the 
inorganic  salts  the  sodium  and  potassium  chlorids  are  the  most  abundant 
and  important. 

The  hydrochloric  acid,  which  exists  in  a  free  state,  is  present  in  variable 
amounts.  In  the  foregoing  table  the  number  of  part  a  thousand  is  much 
smaller  than  is  usually  stated.  According  to  most  observers,  hydrochloric 
acid  is  present  to  the  extent  of  from  0.2  to  0.3  part  a  hundred.  Though 
secreted  as  soon  as  the  food  enters  the  stomach,  the  acid  can  not  be 
detected  in  the  free  state  until  after  the  lapse  of  from  thirty  to  forty  minutes. 
It  acidulates  the  food  and  prevents  fermentative  changes. 

TYlg.  pepsin,  which  is  present  in  gastric  juice  associated  with  the  organic 
matter,  is  a  hydrolytic  ferment  or  enzyme.  When  freed  from  its  associa- 
tions and  obtained  in  a  pure  state,  pepsin  presents  the  characteristics  of  a 
colloid  body,  and  resembles  in  its  reactions  the  albuminoids.  It  has  the 
power,  when  brought  into  relation  with  acidulated  proteids,  of  transform- 
ing them  into  new  forms  capable  of  absorption  into  the  blood. 

Rennin. — In  addition  to  pepsin  a  second  ferment  exists  in  the  gastric 
juice,  to  which  the  term  rennin  has  been  given.  It  possesses  the  power  of 
coagulating  the  caseinogen  of  milk.  It  exists  in  the  mucous  membrane, 
from  which  it  can  be  extracted  by  appropriate  means.  When  rennin  acts 
on  caseinogen,  the  latter  is  split  into  insoluble  casein  and  a  soluble  albumin. 
Calcium  phosphate  is  essential  to  the  action  of  this  enzyme. 

Gastric  Glands. — Embedded  within  the  mucous  membrane  are  to  be 
found  enormous  numbers  of  tubular  glands,  which,  though  resembling  one 


102 


HUMAN    PHYSIOLOGY. 


another  in  general  form,  differ  in  their  histologic  details  in  various  por- 
tions of  the  stomach. 

In  the  cardiac  end  or  fundus  the  glands  consist  of  several  long  tubules, 
opening  into  a  short,  common  duct,  which  opens  by  a  wide  mouth  on 
the  surface  of  the  mucous  membrane.  Each  gland  consists  primarily  of  a 
basement  membrane  lined  by  epithelial  cells.  In  the  duct  the  epithelium 
is  of  the  columnar  variety,  resembling  that  covering  the  surface  of  the 
mucous  membrane.  The  secretory  portion  of  the  tubule  is  lined  by  a  layer 
of  short,  polyhedral,  granular,  and  nucleated  cells,  which,  as  they  border 
the  lumen  of  the  tubule,  and  thus  occupy  the  central  portion  of  the  gland, 
are  termed  central  cells.     At  irregular  intervals,  between  the  central  cells 


Fig.  13. 
Diagram  showing  the  relation  of  the  ultimate  twigs  of  the  blood-vessels,  V  and  A,  and 
of  the  absorbent  radicles   to  the  glands  of  the  stomach  and  the  different  kinds  of 
-  epithelium — viz.,  above  cyiindric  cells  ;  small,  pale  eel  sin  the  lumen,  outside  which 
are  the  dark  ovoid  cells. — (  Yeo's"  Text-book  0/ Physiology.'") 


and  the  wall  of  the  tubule,  are  found  large,  oval,  reticulated  cells,  which, 
on  account  of  their  position,  are  termed  parietal  cells.      (See  Fig.  13.) 

Each  parietal  cell  is  in  relation  with  a  system  of  fine  canals,  which  open 
directly  into  the  lumen  of  the  gland.     It  is  estimated  that  the  fundus  con- 


DIGESTION.  103 

tains  about  five  million  glands.  In  the  pyloric  end  of  the  stomach  the 
glands  are  generally  branched  at  their  lower  extremities,  and  the  common 
duct  is  long  and  wide.  The  duct  is  lined  by  columnar  epithelium,  while 
the  secreting  part  is  lined  by  short,  slightly  columnar,  granular  cells.  The 
parietal  cells  are  entirely  wanting.  The  epithelium  covering  the  surface 
of  the  mucous  membrane  is  tall,  narrow  and  cylindric  in  shape,  and  con- 
sists of  mucus-secreting  goblet  cells.  The  outer  half  of  the  cell  contains  a 
substance,  mucinogen,  which  produces  mucin.  The  gastric  glands  in  both 
situations  are  surrounded  by  a  fine  connective  tissue,  which  supports 
blood-vessels,  nerves,  and  lymphatics. 

Changes  in  the  Cells  During  Secretion. — During  the  periods  of  rest 
and  secretory  activity  the  cells  of  the  glands  undergo  changes  in  structure 
which  are  supposed  to  be  connected  with  the  production  of  the  pepsin  and 
hydrochloric  acid.  During  rest,  the  protoplasm  of  the  central  cells  becomes 
filled  with  granular  matter  ;  during  the  time  of  secretion  this  disappears, 
presumably  passing  into  the  lumen  of  the  tubule,  and  as  a  result  the  proto- 
plasm becomes  clear  and  hyaline  in  appearance.  The  granular  material 
is  probably  the  mother  substance,  pepsinogen,  which,  inactive  in  itself, 
yields  the  active  ferment,  pepsin.  The  parietal  cells  during  digestion  in- 
crease in  size,  but  do  not  become  granular.  It  is  at  this  period  that  they 
secrete  the  hydrochloric  acid.  After  digestion  they  rapidly  diminish  in 
size  and  return  to  their  former  condition.  The  pyloric  glands  secrete 
pepsin  only. 

Mechanism  of  Secretion. — In  the  intervals  of  digestion  the  mucous 
membrane  of  the  stomach  is  covered  with  a  layer  of  mucus.  As  soon  as 
the  food  passes  from  the  esophagus  into  the  stomach,  the  blood-vessels 
dilate,  the  circulation  becomes  more  active,  and  the  membrane  assumes  a 
bright  red  appearance.  Coinciden tally,  small  drops  of  gastric  juice  begin 
to  exude  from  the  glands,  which,  as  they  increase  in  number,  run  together 
and  trickle  down  the  sides  of  the  stomach.  This  pouring  out  of  fluid  con- 
tinues during  the  presence  of  food  in  the  stomach. 

The  secretion  of  gastric  juice  is  a  reflex  act,  taking  place  through  the 
central  nervous  system  and  called  forth  in  response  to  the  stimulus  of  food 
in  the  stomach.  That  the  central  nervous  system  also  directly  influences 
the  production  of  the  secretion  is  shown  by  the  fact  that  emotion,  such 
as  fear  or  anger,  will  arrest  or  vitiate  the  normal  secretion.  The  reflex 
nature  of  the  process  can  be  shown  by  experimentation  upon  the  pneu- 
mogastric  nerve.  If  during  digestion,  when  the  peristaltic  movements  are 
active  and  the  gastric  mucous  membrane  is  flushed  and  covered  with  gas- 


104  HUMAN    PHYSIOLOGY. 

trie  juice,  the  pneumogastric  nerves  are  divided  on  both  sides,  the  mucous 
membrane  becomes  pale,  the  secretion  is  arrested,  and  the  peristaltic  move- 
ments become  less  marked.  Stimulation  of  the  peripheral  end  produces 
no  constant  effects  ;  stimulation  of  the  central  end,  however,  is  at  once 
followed  by  dilatation  of  the  vessels,  flushing  of  the  mucous  membrane, 
and  reestablishment  of  the  secretion.  It  is  evident,  therefore,  that  during 
digestion  afferent  impulses  are  passing  up  the  pneumogastrics  to  the  med- 
ulla ;  efferent  impulses,  in  all  probability,  pass  through  the  fibers  of  the 
sympathetic  nervous  system  to  the  blood-vessels  and  glands  concerned  in 
the  elaboration  of  the  gastric  juice.  After  all  the  nerve  connections  of 
the  stomach  are  divided,  the  secretion  of  a  small  quantity  of  juice  continues 
for  several  days.  This  has  been  attributed  to  the  action  of  a  local  nervous 
mechanism  and  to  the  direct  action  of  the  food  upon  the  protoplasm  of  the 
secreting  cells. 

Chemic  Action  of  the  Gastric  Juice. — By  the  combined  influence  of 
the  contraction  of  the  muscular  walls,  the  action  of  the  gastric  juice,  and 
the  temperature,  the  food  is  reduced  to  a  semiliquid  condition  and  acquires 
a  distinct  acid  odor.  This  semifluid  mass  will  vary  in  composition  and 
appearance  according  to  the  nature  of  the  food.  To  this  matter  the  term 
chyme  has  been  given. 

Meat  is  rapidly  disintegrated  by  the  solution  of  its  connective  tissue. 
The  fibers  thus  separated  are  readily  broken  up  into  particles  by  solution 
of  the  sarcolemma.  Well-cooked  meat  is  more  easily  digested,  owing  to 
the  conversion  of  the  connective  tissue  into  gelatin. 

Connective  tissues  in  the  raw  or  imperfectly  gelatinized  condition  are 
very  slowly  dissolved.  Cartilage,  tendons,  and  even  bones  will  in  time  be 
corroded  and  liquefied. 

Vegetables  are  not  easily  digested  unless  thoroughly  prepared  by  sufficient 
cooking.  The  nutritive  principles  are  inclosed  by  cellulose  walls,  which 
are  not  affected  by  gastric  juice.  The  influence  of  heat  and  moisture 
softens  and  ruptures  the  cellulose  walls  so  as  to  permit  the  introduction  of 
gastric  juice  and  the  solution  of  its  nutritive  principles. 

The  principal  action  of  the  gastric  juice,  however,  is  the  transforma- 
tion of  the  different  proteid  principles  of  the  food  into  peptones,  the  inter- 
mediate stages  of  which  are  due  to  the  influence  of  the  acid  and  pepsin  re- 
spectively. As  soon  as  any  one  of  the  albumins  is  penetrated  by  the  acid 
it  is  converted  into  acid-albumin,  a  fact  which  indicates  that  the  first  step 
in  gastric  digestion  is  the  acidification  of  the  proteids.  This  having  been 
accomplished,  the  pepsin  becomes  operative  and  In  a  varying  length  gf 


DIGESTION.  105 

time  transforms  the  acid- albumin  into  a  new  form  of  proteid'  termed  pep- 
tone, of  which,  as  indicated  by  chemic  tests,  there  are  probably  two  forms, 
hemi-  and  anti-peptone.  In  this  transformation  it  is  possible  to  isolate  inter- 
mediate bodies  by  the  addition  of  ammonium  sulphate,  to  which  the  term 
albumose  or  proteose  has  been  given.  Inasmuch  as  two  forms  of  peptone 
can  be  isolated  after  complete  digestion  of  any  given  proteid,  it  is  assumed, 
from  this  and  other  facts,  that  their  appearance  has  been  preceded  by  two 
forms  of  albumose,  hemi-  and  anti-.  This  supposed  change  is  represented 
in  the  following  scheme  : 

Albumin. 

I 
Acid-albumin. 

/\ 
Hemi- albumose.     Anti-albumose. 

I 
Hemi-peptone.       Anti-peptone. 

From  the  fact  that  one  form  of  peptone — hemi — under  the  influence  of 
the  pancreatic  ferment  trypsin  can  be  decomposed  into  leucin,  tyrosin, 
aspartic  acid,  etc.,  it  is  believed  that  all  the  simple  proteids  contain  two 
distinct  groups  or  radicles  termed  hemi-  and  anti-radicles,  and  that  it  is 
this  fact  that  determines  the  line  of  cleavage  and  the  characteristics  of  the 
cleavage  products. 

Peptones. — Peptones  are  the  final  products  of  the  digestion  of  proteid 
bodies,  and  differ  from  the  bodies  from  which  they  are  derived  in  the 
following  particulars : 

1.  They  are  diffusible, — i.  e.,  capable  of  passing  readily  through  animal 
membranes, — a  condition  essential  for  their  absorption. 

2.  They  are  soluble  in  water  and  in  saline  solution. 

3.  They  are  non-coagulable  by  heat  and  nitric  or  acetic  acids.  They 
can  be  readily  precipitated,  however,  by  tannic  acid,  by  bile  acids,  and 
by  mercuric  chlorid. 

4.  They  are  absorbable  and  assimilab  'e,  soon  becoming  transformed  into 
serum -album  in. 

The  duration  of  gastric  digestion  will  depend  largely  upon  the  quantity 
and  quality  of  the  food.  The  digestion  of  the  average  meal  occupies  from 
three  to  five  hours. 

Movements  of  the  Stomach. — As  soon  as  digestion  commences  the 

cardiac  and  pyloric  orifices  are  closed ;  the  walls  of  the  stomach  contract 

upon  the  food,  and  a  peristaltic  action  begins,  which  carries  the  food  along 

the  greater  and  lesser  curvatures,  and  thoroughly  incorporates  it  with  the 

8 


106  HUMAN    PHYSIOLOGY. 

gastric  juice.     As  soon  as  any  portion  of  the  food  is  digested,  it  passes 
through  the  pylorus  into  the  intestine. 

TABLE   SHOWING   DIGESTIBILITY    OF   VARIOUS   ARTICLES    OF   FOOD. 

Hours.     Minutes. 

Eggs,  whipped, I  20 

"      soft-boiled, 3 

"      hard-boiled, 3  30 

Oysters   raw, 2  55 

"       stewed,        3  30 

Lamb,  broiled, 2  30 

Veal,         "  .  \ 4 

Pork,  roasted, 5  15 

Beefsteak,  broiled, 3 

Turkey,  roasted, 2  25 

Chicken,  boiled 4 

"         fricasseed,         .2  45 

Duck,  roasted 4 

Soup,  barley,  boiled,  ,    .    .    .    , I  30 

"      bean,        "         , 3 

"      chicken,  "  . 3 

"      mutton,   "          .3  30 

Liver,  beef,  broiled, 2 

Sausage,              " 3  20 

Green  corn,  boiled 3  45 

Beans,                " 2  30 

Potatoes,  roasted 2  30 

"        boiled, 3  30 

Cabbage,     "        4  30 

Turnips,       "             3  30 

Beets,           "        ...                3  45 

Parsnips,      "            •  .    .    .  2  30 


INTESTJNAL  DIGESTION. 

The  process  of  digestion  as  it  takes  place  in  the  small  intestine  is  ex- 
ceedingly important  and  complex,  and  is  brought  about  by  the  action  of 
the  pancreatic  juice,  the  bile,  and  the  intestinal  juice. 

The  contents  of  the  stomach  at  the  close  of  gastric  digestion  consist  of 
water,  inorganic  salts,  peptones,  undigested  albumins  and  starches,  maltose, 
cane-sugar,  liquefied  fats,  cellulose,  and  the  indigestible  portions  of  meats, 
cereals,  fruits,  etc.  This  so-called  chyme  is  quite  acid  in  reaction,  and  upon 
its  passage  through  the  now  open  pylorus  into  the  intestine  it  excites  a  reflex 
stimulation  and  secretion  of  the  intestinal  fluids,  which  are  decidedly 
alkaline  in  reaction,  and  which  have  a  neutralizing  action  on  the  chyme. 
As  soon  as  the  latter  becomes  alkaline  and  gastric  digestion  is  arrested,  the 


DIGESTION.  107 

various  phases  of  intestinal  digestion  begin  which  eventuate  in  the  trans- 
formation of  all  the  remaining  undigested  nutritive  materials  into  absorb- 
able and  assimilable  compounds. 

The  small  intestine  is  about  22  feet  in  length  and  about  1^  inches 
in  diameter.     Like  the  stomach,  it  possesses  three  coats,  as  follows  : 

1.  The  serous,  or  peritoneal. 

2.  The  muscular,  the  fibers  of  which  are  arranged  for  the  most  part  cir- 
cularly. Some  of  the  fibers  are  so  arranged  as  to  form  longitudinal 
bands. 

3.  The  mucous,  which  presents  a  series  of  transverse  folds,  known  as  the 
valvulcc  conniventes. 

Intestinal  Glands. — In  that  portion  of  the  small  intestine  known  as 
the  duodenum  are  to  be  found  a  number  of  small,  branched,  tubular  glands 
(Brunner's),  the  acini  of  which  are  lined  by  short,  cylindric  cells,  similar 
to  those  lining  the  pyloric  glands.  From  the  duodenum  to  the  termination 
of  the  intestine  the  mucous  membrane  contains  an  enormous  number  of 
tubular  glands  (Lieberkiihn's),  formed  by  an  inversion  of  the  basement 
membrane  and  lined  by  epithelial  cells.  The  common  secretion  of  these 
intestinal  glands  forms  the  intestinal  juice.  This  is  a  thin,  opalescent, 
slightly  yellowish  fluid,  alkaline  in  reaction,  and  contains  water,  salts,  and 
proteid  matter. 

The  function  of  the  intestinal  juice  is  but  incompletely  known.  It  ap- 
pears to  have  the  power  of  converting  starch  into  dextrose  ;  it  is  doubtful 
whether  it  is  capable  of  digesting  either  albumins  or  fats.  Its  most  dis- 
tinctive action  is  the  inversion  of  cane-sugar,  maltose,  and  lactose  into 
dextrose,  thus  preparing  them  for  absorption.  This  change  is  dependent 
on  the  presence  of  a  ferment  body  known  as  invertin. 

The  pancreatic  juice  is  secreted  by  the  pancreas,  a  flattened  gland, 
about  six  inches  long,  running  transversely  across  the  posterior  wall  of  the 
abdomen  behind  the  stomach  ;  its  duct  opens  into  the  duodenum. 

The  pancreas  is  similar  in  structure  to  the  salivary  glands,  and  consists 
of  a  system  of  ducts  terminating  in  acini.  The  acini  are  tubular  or  flask- 
shaped,  and  consist  of  a  basement  membrane  lined  by  a  layer  of  cylindric, 
conic  cells,  which  encroach  upon  the  lumen  of  the  acini.  The  cells 
exhibit  a  difference  in  their  structure  (Fig.  14),  and  may  be  said  to  consist 
of  two  zones — viz.,  an  outer  parietal  zone,  which  is  transparent  and  appar- 
ently homogeneous,  staining  rapidly  with  carmin  ;  an  inner  zone,  which 
borders  the  lumen,  and  is  distinctly  granular  and  stains  but  slightly  with 
carmin.     These  cells  undergo  changes  similar  to  those  exhibited  by  the 


108 


HUMAN    PHYSIOLOGY. 


cells  of  the  salivary  glands  during  and  after  active  secretion.  As  soon  as 
the  secretory  activity  of  the  pancreas  is  established,  the  granules  disappear, 
and  the  inner  granular  layer  becomes  reduced  to  a, very  narrow  border, 
while  the  outer  zone  increases  in  size  and  occupies  nearly  the  entire  cell. 
During  the  intervals  of  secretion,  however,  the  granular  layer  reappears 
and  increases  in  size  until  the  outer  zone  is  reduced  to  a  minimum.  It 
would  seem  that  the  granular  matter  is  formed  by  the  nutritive  processes 
occurring  in  the  gland  during  rest,  and  is  discharged  during  secretory 
activity  into  the  ducts,  and  takes  part  in  the  formation  of  the  pancreatic 
secretion. 

The  pancreatic  juice  is  transparent,  colorless,  strongly   alkaline,  and 
viscid,  and   has  a  specific  gravity  of  1040.     It  is  one  of  the  most  im- 


■*' 

A  B 

Fig.  14. — One  Saccule  of  the  Pancreas  of  the  Rabbit  in  Different  States 
of  Activity. — (  Yeo's  "  Text-book  of  Physiology ,"  after  Kilhne  and  Lea.) 

A.  After  a  period  of  rest,  in  which  case  the  outlines  of  ihe  cells  are  indistinct  and  the 
inner  zone — i.  e.,  the  part  of  the  cells  (a)  next  the  lumen  (c) — is  broad  and  filled 
with  fine  granules.  B.  After  the  gland  has  poured  out  its  secretion,  when  the  cell 
outlines  (d)  are  clearer,  the  granular  zone  (a)  is  smaller,  and  the  clear  outer  zone  is 
wider. 

portant  of  the  digestive  fluids,  as  it  exerts  a  transforming  influence  upon 
all  classes  of  alimentary  principles,  and  has  been  shown  to  contain  at  least 
three  distinct  ferments.      It  has  the  following  composition  : 

COMPOSITION    OF    PANCREATIC   JUICE. 

Water, 900.76 

Albuminoid  substances, .    90.44        * 

Inorganic  salts, 8.80 

1,000.00 
The  pancreatic  juice  is  characterized  by  its  action  : 
I.   Upon  starch.     When  starch  is  subjected  to  the  action  of  the  juice,  it 
is  at  once  transformed  into  maltose  ;  the  change  takes  place  more  rapidly 


DIGESTION.  109 

than  when  saliva  is  added.     This  action  is  caused  by  the  presence  of  a 
special  ferment,  amylopsin. 

2.  Upon  albumin.  The  proteid  bodies  which  escape  digestion  in  the 
stomach  are  converted  into  peptones  by  the  action  of  the  alkali  and  fer- 
ment. The  first  effect  of  the  alkali  is  to  change  the  proteid  into  an 
alkali-albumin,  a  fact  which  indicates  that  in  the  digestion  of  albumin 
by  pancreatic  juice,  the  first  stage  is  alkalinization.  This  having  been 
accomplished,  the  ferment  trypsin  transforms  the  alkali-albumin  into 
peptone,  of  which,  as  in  gastric  digestion,  there  are  two  forms,  hemi-  and 
a7iti -peptone.  For  the  same  reason  it  is  believed  that  here  also  these 
bodies  are  preceded  in  their  development  by  albumoses,  of  which  there 
are  probably  two  forms.  Long-continued  action  of  the  pancreatic  juice 
as  previously  stated,  decomposes  the  hemi-peptone  intoleucin,  tyrosin,  etc. 

3.  Xlpoxi  fats.  The  most  striking  action  of  the  pancreatic  juice  is  the  emul- 
sification  of  the  fats  or  their  subdivision  into  minute  particles  of  micro- 
scopic size.  This  change  takes  place  rapidly,  and  depends  upon  the 
alkalinity  of  the  fluid  and  the  quantity  of  albumin  present,  combined  with 
the  intestinal  movements.  The  neutral  fats  are  also  decomposed  into 
their  corresponding  fatty  acids  and  glycerin  ;  the  acids  thus  set  free  unite 
with  the  alkaline  bases  present  in  the  intestine  and  form  soaps.  This 
decomposition  of  the  neutral  fats  is  caused  by  the  ferment,  sleapsin. 

The  bile  has  an  important  function  in  the  elaboration  of  the  food  and  in 
its  preparation  for  absorption.  It  is  a  golden-brown,  viscid  fluid,  having  a 
neutral  or  alkaline  reaction  and  a  specific  gravity  of  1 020. 

COMPOSITION    OF   BILE. 

Water,        859.2 

Sodium  glycocholate,  1  or .4 

Sodium  taurocholate,  J 

Fat,  9.2 

Cholesterin,  ....  2.6 

Mucus  and  coloring-matter, 29  8 

Salts, 7-8 

1,000.0 

The  biliary  salts,  sodium  glycocholate  and  taurocholate,  are  characteristic 
ingredients,  and  by  the  process  of  secretion  are  formed  in  the  liver  from 
materials  furnished  by  the  blood.  It  is  probable  that  they  are  derived  from 
the  nitrogenized  compounds,  though  the  stages  in  the  process  are  unknown. 
They  are  reabsorbed  from  the  small  intestine  to  play  some  ulterior  part 
in  nutrition. 

Cholesterin  is  a  product  of  waste  taken  up  by  the  blood  from  the  nerve 
tissues  and  excreted  by  the  liver.     It  crystallizes  in  the  form  of  rhombic 


110  HUMAN    PHYSIOLOGY. 

plates,  which  are  quite  transparent.  When  retained  within  the  blood,  it 
gives  rise  to  the  condition  of  cholesteremia,  attended  with  severe  nervous 
symptoms.      It  is  given  off  in  the  feces  under  the  form  of  stercorin. 

The  coloring-matters  which  give  the  tints  to  the  bile  are  biliverdin  and 
bilirubin,  and  are  probably  derived  from  the  coloring-matter  of  the  blood. 
Their  presence  in  any  fluid  can  be  recognized  by  adding  to  it  nitric  acid 
containing  nitrous  acid,  when  a  play  of  colors  is  observed,  beginning  with 
green,  blue,  violet,  red,  and  yellow. 

The  bile  is  both  a  secretion  and  an  excretion  ;  it  is  constantly  being 
formed  and  discharged  by  the  hepatic  ducts  into  the  gall-bladder,  in  which 
it  is  stored  up  during  the  intervals  of  digestion.  As  soon  as  food  enters  the 
intestines  it  is  poured  out  abundantly  by  the  contraction  of  the  walls  of  the 
gall-bladder. 

The  amount  secreted  in  twenty-four  hours  is  about  2j^  pounds. 

Functions  of  the  Bile  : 

1.  It  assists  in  the  enmhification  of  the  fats  and  promotes  their  absorption. 

2.  It  tends  to  prevent  putrefactive  changes  in  the  food. 

3.  It  stimulates  the  secretion  of  the  intestinal   glands,  and   excites  the 
normal  peristaltic  movement  of  the  bowels. 

The  digested  food,  the  chyme,  is  a  grayish,  pultaceous  mass,  but  as  it 
passes  through  the  intestines  it  becomes  yellow  from  admixture  with  the 
bile.  It  is  propelled  onward  by  vermicular  motion  —  by  the  contraction  of 
the  circular  and  longitudinal  muscle-fibers. 

During  the  passage  of  the  digesting  food  through  the  intestinal  canal  the 
nutritive  products  —  the  peptones,  the  dextrose  and  levulose,  the  fatty  emul- 
sions, the  fatty  acids  and  their  soaps  —  are  absorbed  into  the  blood,  while 
the  undigested  residue  is  carried  onward  by  the  peristaltic  movements 
through  the  ileo-cecal  valve  into  the  large  intestine. 

Intestinal  Fermentation.  —  Owing  to  the  favorable  conditions  for 
fermentative  and  putrefactive  processes — e.g.,  heat,  moisture,  oxygen,  micro- 
organisms —  the  food,  when  consumed  in  excessive  quantity  or  when  acted 
upen  by  defective  secretions,  undergoes  a  series  of  decomposition  changes 
which  are  attended  by  the  production  of  gases  and  various  chemic  com- 
pounds. Grape-sugar  and  maltose  are  partially  split  into  lactic  acid,  this 
into  butyric  acid,  carbon  dioxid,  and  hydrogen.  Fats  are  reduced  to 
glycerol  and  fatty  acids  ;  the  glycerol,  according  to  the  organisms  present, 
yields  succinic  and  other  fatty  acids,  carbon  dioxid,  and  hydrogen. 

The  proteids,  under  the  prolonged  action  of  the  pancreatic  juice,  are 
decomposed,  and  yield  leucin  and  tyrosin  ;  the  former  is  split  into  valerianic 


ABSORPTION.  HI 

acid,  ammonia,  and  carbon  dioxid  ;  the  latter  is  split  into  indol,  which  is 
the  antecedent  of  indican  in  the  urine.  Skatol  is  another  proteid  deriva- 
tive constantly  present  in  the  fecal  substance. 

The  large  intestine  extends  from  the  ileo-cecal  valve  to  the  anus,  and 
is  about  five  feet  in  length.  Like  the  stomach  it  consists  of  three  coats  : 
the  serous,  the  muscular,  and  mucous.  The  mucous  membrane  contains  a 
number  of  mucous  glands,  the  secretion  from  which  lubricates  the  surface 
of  the  canal.  The  ascending  portion  of  the  large  intestine  possesses  the 
power  of  absorption,  and  hence  its  contents  become  less  liquid  and  more 
consistent.  As  the  residue  passes  toward  the  sigmoid  flexure  it  acquires 
the  characteristics  of  fecal  matter.  This  residue  consists  of  the  undigested 
portions  of  the  food,  decomposition  products,  mucus,  and  inorganic  salts. 

Defecation  is  the  voluntary  act  of  extruding  the  feces  from  the  rectum, 
and  is  accomplished  by  a  relaxation  of  the  sphincter  ani  muscle  and  by 
the  contraction  of  the  muscular  walls  of  the  rectum,  aided  by  the  contrac- 
tion of  the  abdominal  muscles. 


ABSORPTION. 

The  term  absorption  is  applied  to  the  passage  gr  transference  of  material 
into  the  blood  from  the  tissues,  from  the  serous  cavities,  and  from  the 
mucous  surfaces  of  the  body.  The  most  important  of  these  surfaces, 
especially  in  its  relation  to  the  formation  of  the  blood,  is  the  mucous  sur- 
face of  the  alimentary  canal  ;  for  it  is  from  this  organ  that  new  materials 
are  derived  which  maintain  the  quality  and  quantity  of  the  blood.  The 
absorption  of  materials  from  the  interstices  of  the  tissues  is  to  be  regarded 
rather  as  a  return  to  the  blood  of  liquid  nutritive  material  which  has 
escaped  from  the  blood-vessels  for  nutritive  purposes,  and  which,  if  not 
returned,  would  lead  to  an  accumulation  of  such  fluid  and  the  develop- 
ment of  dropsical  conditions. 

The  anatomic  mechanisms  involved  in  the  absorptive  process  are,  pri- 
marily, the  lymph-spaces,  the  lymph- capillaries,  and  the  blood-capillaries ; 
secondarily,  the  lymphatic  vessels  and  larger  blood-vessels. 

Lymph-spaces,  Lymph-capillaries,  Blood-capillaries. — Every- 
where throughout  the  body,  in  the  intervals  between  connective-tissue  bun- 
dles and  in  the  interstices  of  the  several  structures  of  which  an  organ  is 
composed,  are  found  spaces  of  irregular  shape  and  size,  determined  largely 
by  the  nature  of  the  organ  in  which  they  are  found,  which  have  been  termed 


112  HUMAN   THYSIOLOGY. 

lymph-spaces  or  lacuna,  from  the  fact  that  during  the  living  condition  they 
are  continually  receiving  the  lymph  which  has  escaped  from  the  blood- 
vessels throughout  the  body.  In  addition  to  the  connective-tissue  lymph- 
spaces,  various  observers  have  described  special  lymph-spaces  in  the 
testicle,  kidney,  liver,  thymus  gland,  and  spleen;  in  all  secreting  glands 
between  the  basement  membrane  and  blood-vessels  ;  around  blood-vessels 
(perivascular  spaces),  and  around  nerves.  The  se>ous  cavities  of  the  body 
— peritoneal,  pleural,  pericardial,  etc. — may  also  be  regarded  as  lymph- 
spaces,  which  are  in  direct  communication  by  open  mouths  or  stomata  with 
the  lymphatic  capillaries.  This  method  of  communication  is  not  only  true 
of  serous  membranes,  but  to  some  extent  also  of  mucous  membranes. 
The  cylindric  sheaths  and  endothelial  cells  surrounding  the  brain,  spinal 
cord,  and  nerves  can  also  be  looked  upon  as  lymph-spaces  in  connection 
with  lymph- capillaries. 

The  lymphatic  capillaries,  in  which  the  lymphatic  vessels  proper  take 
their  origin,  are  arranged  in  the  form  of  plexuses  of  quite  irregular  shape. 
In  most  situations  they  are  intimately  interwoven  with  the  blood-vessels, 
from  which,  however,  they  can  be  readily  distinguished  by  their  larger 
caliber  and  irregular  expansions.  The  wall  of  the  lymph-capillary  is 
formed  by  a  single  layer  of  epithelioid  cells,  with  sinuous  outlines,  and 
which  accurately  dovetail  with  one  another.  In  no  instance  are  valves 
found.  In  the  villus  of  the  small  intestine  the  beginning  of  the  lymphatic 
is  to  be  regarded  as  a  lymph-capillary,  generally  club-shaped,  which  at  the 
base  of  the  villus  enters  a  true  lymphatic ;  at  this  point  a  valve  is  situated, 
which  prevents  regurgitation.  The  lymphatic  capillaries  anastomose  freely 
with  one  another,  and  communicate  on  the  one  hand  with  the  lymph- spaces, 
and  on  the  other  with  the  lymphatic  vessels  proper. 

As  the  shape,  size,  etc.,  of  both  lymph-spaces  and  capillaries  are  deter- 
mined largely  by  the  nature  of  the  tissues  in  which  they  are  contained,  it 
is  not  always  possible  to  separate  the  one  from  the  other.  Their  function, 
however,  may  be  regarded  as  similar — viz.,  the  collection  of  the  lymph 
which  has  escaped  from  the  blood-vessels,  and  its  transmission  onward  into 
the  regular  lymphatic  vessels. 

The  blood-capillaries  not  only  permit  the  escape  of  the  liquid  nutritive 
portions  of  the  blood  through  their  delicate  walls,  but  are  also  engaged  in 
the  reabsorption  of  this  transudate,  as  well  as  in  the  absorption  of  new 
materials  from  the  alimentary  canal.  The  extensive  capillary  network 
which  is  formed  by  the  ultimate  subdivision  of  the  arterioles  in  the  sub- 
mucous tissue  and  villi  of  the  small  intestine  forms  an  anatomic  arrange- 
ment well   adapted   for  absorption.      It   is  now  well  known  that   in  the 


ABSORPTION.  113 

absorption  of  the  products  of  digestion  the  blood-capillaries  are  more  active 
than  the  lymphatic  capillaries. 

Lymphatic  Vessels. — These  constitute  a  system  of  minute,  delicate 
transparent  vessels,  found  in  nearly  all  the  organs  and  tissues  of  the 
body.  Having  their  origin  at  the  periphery  in  the  lymphatic  capillaries 
and  spaces,  they  rapidly  converge  toward  the  trunk  of  the  body  and 
empty  into  the  thoracic  duct.  In  their  course  they  pass  through  numerous 
small  ovoid  bodies,  the  lymphatic  glands. 

The  lymphatic  vessels  of  the  small  intestines — the  lacteah — arise  within 
the  villous  processes  which  project  from  the  inner  surface  of  the  intestine 
throughout  its  entire  extent.  The  wall  of  the  villus  is  formed  by  an  eleva- 
tion of  the  basement  membrane,  and  is  covered  by  a  layer  of  columnar 
epithelial  cells.  The  basis  of  the  villus  consists  of  adenoid  tissue,  a  fine 
plexus  of  blood-vessels,  unstriped  muscle-fibers,  and  the  lacteal  vessel. 
The  adenoid  tissue  consists  of  a  number  of  intercommunicating  spaces, 
containing  leukocytes.  The  lacteal  vessel  possesses  a  thin  but  distinct 
wall  composed  of  endothelial  plates,  with  here  and  there  openings  which 
bring  the  interior  of  the  villus  into  communication  with  the  spaces  of  the 
adenoid  tissue. 

The  structure  of  the  larger  vessels  resembles  that  of  the  veins,  consisting 
of  three  coats  : 

1.  External,  composed  of  fibrous  tissue  and  muscle-fibers,  arranged  longi- 
tudinally. 

2.  Middle,  consisting  of  white  fibers  and  yellow  elastic  tissue,  non-striated 
muscle-fibers,  arranged  transversely. 

3.  Internal,  composed  of  an  elastic  membrane,  lined  by  endothelial  cells. 
Throughout  their  course  are  found  numerous  semilunar  valves,  opening 

toward  the   larger   vessels,  formed   by  a   folding  of  the  inner  coat  and 
strengthened  by  connective  tissue. 

Lymphatic  Glands. — The  lymphatic  glands  consist  of  an  external 
capsule  composed  of  fibrous  tissue  which  contains  non  striped  muscle- 
fibers  ;  from  its  inner  surface  septa  of  fibrous  tissue  pass  inward  and  sub- 
divide the  gland-substance  into  a  series  of  compartments,  which  communi- 
cate with  one  another.  The  blood-vessels  which  penetrate  the  gland  are 
surrounded  by  fine  threads,  forming  a  follicular  arrangement,  the  meshes  of 
which  contain  numerous  lymph-corpuscles.  Between  the  follicular  threads 
and  the  wall  of  the  gland  lies  a  lymph-channel  traversed  by  a  reticulum  of 
adenoid  tissue.  The  lymphatic  vessels,  after  penetrating  this  capsule,  pour 
their  lymph  into  this  channel,  through  which  it  passes  ;  it  is  then  collected 


114 


HUMAN    PHYSIOLOGY. 


Fig. 


-Diagram   Showing  the   Course   of  the  Main  Trunks   of  the 
Absorbent  System.— (  Yeo's  "  Text-Book  of  Physiology.") 


The  lymphatics  of  lower  extremities  (D)  meet  the  lacteals  of  intestines  (LAC)  at  the 
receptaculum  chyli  (RC),  where  the  thoracic  duct  begins.  The  superficial  vessels 
are  shown  in  the  diagram  on  the  right  arm  and  leg  (S),  and  the  deeper  ones  on  the 
arm  to  the  left  (D).  The  glands  are  here  and  there  shown  in  groups.  The  small 
right  duct  opens  into  the  veins  on  the  right  side.  The  thoracic  duct  opens  into  the 
union  of  the  great  veins  of  the  left  side  of  the  neck  (T). 


ABSORPTION.  115 

by  the  efferent  vessels  and  transmitted  onward.  The  lymph- corpuscles 
which  are  washed  out  of  the  gland  into  the  lymph-stream  are  formed,  most 
probably,  by  division  of  preexisting  cells. 

The  thoracic  duct  is  the  general  trunk  of  the  lymphatic  system  ;  into 
it  the  vessels  of  the  lower  extremities,  of  the  abdominal  organs,  of  the  left 
side  of  the  head,  and  of  the  left  arm  empty  their  contents.  It  is  about  twenty 
inches  in  length,  arises  in  the  abdomen,  opposite  the  third  lumbar  vertebra, 
by  a  dilatation  (the  receptaculum  chyli),  ascends  along  the  vertebral  column 
to  the  seventh  cervical  vertebra,  and  terminates  in  the  venous  system  at 
the  junction  of  the  internal  jugular  and  subclavian  veins  on  the  left  side. 
The  lymphatics  of  the  right  side  of  the  head,  of  the  right  arm,  and  of  the 
right  side  of  the  thorax  terminate  in  the  right  thoracic  duct,  about  one 
inch  in  length,  which  joins  the  venous  system  at  the  junction  of  the  internal 
jugular  and  subclavian  on  the  right  side. 

The  general  arrangement  of  the  lymphatic  vessels  is  show  in  figure  15. 

The  blood-vessels  which  are  concerned  in  the  conduction  of  fresh 
nutritive  material  from  the  alimentary  canal  have  their  origin  in  the  elabo- 
rate capillary  network  in  the  mucous  membrane.  The  small  veins  which 
emerge  from  the  network  gradually  unite,  forming  larger  and  larger  trunks, 
which  are  known  as  the  gastric,  superior,  and  inferior  mesenteric  veins. 
These  finally  unite  to  form  the  portal  vein,  a  short  trunk  about  three  inches 
in  length.  The  portal  vein  enters  the  liver  at  the  transverse  fissure,  after 
which  it  forms  a  fine  capillary  plexus  ramifying  throughout  the  substance 
of  the  liver ;  from  this  plexus  the  hepatic  veins  take  their  origin,  and 
finally  empty  the  blood  into  the  vena  cava  inferior.      (See  Fig.  16. ) 

Absorption  of  Food. — Physiological  experiments  have  demonstrated 
that  the  agents  concerned  in  the  absorption  of  new  materials  from  the  ali- 
mentary canal  are  : 

1.  The  blood-vessels  of  the  entire  canal,  but  more  particularly  those  uniting 
to  form  the  portal  vein. 

2.  The  lymphatics  coming  from   the  small  intestine,  which   converge  to 
empty  into  the  thoracic  duct. 

As  a  result  of  the  action  of  the  digestive  fluids  upon  the  different  classes 
of  food  principles — albumins,  sugars,  starches,  and  fats  —  there  are  formed 
peptones,  glucose,  and  fatty  emulsion,  which  differ  from  the  former  in  being 
highly  diffusible — a  condition  essential  to  their  absorption.  In  order  that 
these  substances  may  get  into  the  blood,  they  must  pass  through  the  layer 
of  cylindric  epithelial  cells  and  the  underlying  basement  membrane,  and 
into  the  lymph-spaces  of  the  villi  and  submucous  tissue.      The  mechanism 


116 


HUMAN    PHYSIOLOGY. 


by  which  the  cells  effect  this  passage  of  the  food  is  but  imperfectly  under- 
stood. Osmosis  and  nitration  are  conditions,  however,  made  use  of  by  the 
cells  in  the  absorptive  process. 

The  products  of  digestion  find  their  way  into  the  general  circulation  by 
two  routes  : 
I.   The  water,  peptones,  glucose,  and  soluble  salts,  after  passing  into  the 


Fig.  16. 

Diagram  of  the  portal  vein  [fiv)  arising  in  the  alimentary  tract  and  spleen  (s), 
and  carrying  the  blood  from  these  organs  to  the  liver. — ( Yeo's  "  Text-book  oj 
Physiology.") 


lymph-spaces  of  the  villi,  pass  through  the  wall  of  the  capillary  blood- 
vessel ;  entering  the  blood,  they  are  carried  to  the  liver  by  the  vessels 
uniting  to  form  the  portal  vein  ;  emerging  from  the  liver,  they  are 
empted  into  the  inferior  vena  cava  by  the  hepatic  vein. 
2.  The  emulsified  fat  enters  the  lymph-capillary  in  the  interior  of  the 
villus  ;    by  the  contraction  of   the    layer  of  muscle-fibers   surrounding 


ABSORPTION.  117 

it  its  contents  are  forced  onward  into  the  lymphatic  vessels  or  lacteal, 
thence  into  the  thoracic  duct,  and  finally  into  the  circulation  at  the 
junction  of  the  internal  jugular  and  subclavian  veins  on  the  left  side. 

Absorption  of  Lymph. — Similar  to  the  absorption  of  food  from  the 
alimentary  canal  is  the  absorption  of  lymph  from  the  lymph -spaces  of  the 
organs  and  tissues.  During  the  passage  of  the  blood  through  the  capillary 
blood-vessels  a  portion  of  the  liquor  sanguinis,  or  plasma,  or  lymph,  passes 
through  the  capillary  wall  out  into  the  lymph-spaces.  The  tissue-cells  are 
thus  bathed  with  this  new  materal  ;  from  it  those  substances  are  selected 
which  are  necessary  for  their  growth,  repair,  and  all  purposes  of  nutrition. 
An  excess  of  nutritive  material,  far  beyond  the  needs  of  the  tissues, 
transudes  from  the  blood-vessels,  and  it  is  this  excess  which  is  absorbed 
by  the  lymphatics  and  returned  to  the  blood  by  the  thoracic  duct.  It  is 
quite  probable,  also,  that  a  portion  of  this  transudate  is  reabsorbed  by  the 
blood-vessels. 

Properties  and  Composition  of  Lymph  and  Chyle. — Lymph,  as 
found  in  the  lymphatic  vessels  of  animals,  is  a  clear,  colorless,  or  opalescent 
fluid,  having  an  alkaline  reaction,  a  saline  taste,  and  a  specific  gravity  of 
about  1040.  It  holds  in  suspension  a  number  of  corpuscles  resembling 
in  their  general  appearance  the  white  corpuscles  of  the  blood.  Their 
number  has  been  estimated  at  8,200  per  cubic  millimeter,  though  the  num- 
ber varies  in  different  portions  of  the  lymphatic  system.  As  the  lymph 
flows  through  the  lymphatic  gland  it  receives  a  large  addition  of  corpuscles. 
Lymph- corpuscles  are  granular  in  structure,  and  measure  ^ttVo  °f  an  inch 
in  diameter.  When  withdrawn  from  the  vessels,  lymph  undergoes  a  spon- 
taneous coagulation  similar  to  that  of  the  blood,  after  which  it  separates  in 
serum  and  clot. 

COMPOSITION    OF    LYMPH. 

Water, 95-536 

Proteids  (serum-albumin,  fibrin-globulin),    ....  1.320 

Extractives  (urea,  sugar,  cholesterin), 1.559 

Fatty  matters, a  trace 

Salts, 0.585 

100.000 

Chyle. — Chyle  is  the  fluid  found  in  the  lymphatic  vessels,  coming  from 
the  small  intestine  after  the  digestion  of  a  meal  containing  fat.  In  the 
intervals  of  digestion  the  fluid  of  these  lymphatics  is  identical  in  all  re- 
spects with  the  lymph  found  in  all  other  regions  of  the  body.     As  soon 


118  HUMAN    PHYSIOLOGY. 

as  the  emulsified  fat  passes  into  the  lymphatic  vessels  and  mingles  with  the 
lymph  it  becomes  milky  white  in  color,  and  the  vessels  which  previously 
were  invisible  become  visible,  and  resemble  white  threads  running  between 
the  layers  of  the  mesentery.  Chyle  has  a  composition  similar  to  that  of 
lymph,  but  it  contains,  in  addition,  numerous  fatty  granules,  each  surrounded 
by  an  albuminous  envelope.  When  examined  microscopically,  the  chyle 
presents  a  fine  molecular  basis,  made  up  of  the  finely  divided  granules  of 
fat. 

COMPOSITION   OF    CHYLE. 

Water, 902.37 

Albumin, 35. 16 

Fibrin,        3.70 

Extractives, 15.65 

Fatty  matters, .  36.01 

Salts, 7. 1 1 

1,000.00 

Forces  Aiding  the  Movement  of  Lymph  and  Chyle. — The  lymph 
and  chyle  are  continually  moving  in  a  progressive  manner  from  the  periph- 
ery or  beginning  of  the  lymphatic  system  to  the  final  termination  of  the 
thoracic  duct.  The  force  which  primarily  determines  the  movement  of  the 
lymph  has  its  origin  in  the  beginnings  of  the  lymphatic  vessels,  and  depends 
upon  the  difference  in  pressure  here  and  the  pressure  in  the  thoracic  duct. 
The  greater  the  quantity  of  fluid  poured  into  the  lymph-spaces,  the  greater 
will  be  the  pressure  and,  consequently,  the  movement.  The  first  move- 
ment of  chyle  is  the  result  of  a  contraction  of  the  muscle-fibers  within  the 
walls  of  the  villus.  At  the  time  of  contraction  the  lymphatic  capillary  is 
compressed  and  shortened,  and  its  contents  are  forced  onward  into  the  true 
lymphatic.  When  the  muscle-fibers  relax,  regurgitation  is  prevented  by 
the  closure  of  the  valve  in  the  lymphatic  at  the  base  of  the  villus. 

As  the  walls  of  the  lymphatic  vessels  contain  muscle-fibers,  when  they 
become  distended  these  fibers  contract  and  assist  materially  in  the  onward 
movement  of  the  fluid. 

The  contraction  of  the  general  muscular  masses  in  all  parts  of  the  body, 
by  exerting  an  intermittent  pressure  upon  the  lymphatics,  also  hastens  the 
current  onward ;  regurgitation  is  prevented  by  the  closure  of  valves  which 
everywhere  line  the  interior  of  the  vessels. 

The  respiratory  movements  aid  the  general  flow  of  both  lymph  and  chyle 
from  the  thoracic  duct  into  the  venous  blood.  During  the  time  of  an  in- 
spiratory movement  the  pressure  within  the_thorax,  but  outside  the  lungs, 


BLOOD.  119 

undergoes  a  diminution  in  proportion  to  the  extent  of  the  movement ;  as  a 
result,  the  fluid  in  the  thoracic  duct  outside  of  the  thorax,  being  under  a 
higher  pressure,  flows  more  rapidly  into  the  venous  system.  At  the  time 
of  an  expiration,  the  pressure  rises  and  the  flow  is  temporarily  impeded, 
only  to  begin  again  at  the  next  inspiration. 


BLOOD. 

The  blood  is  a  nutritive  fluid  containing  all  the  elements  necessary  for 
the  repair  of  the  tissues  ;  it  also  contains  principles  of  waste  absorbed  from 
the  tissues,  which  are  conveyed  to  the  various  excretory  organs  and  by  them 
eliminated  from  the  body. 

The  total  amount  of  blood  in  the  body  is  estimated  to  be  about  one  eighth 
of  the  body-weight ;  from  sixteen  to  eighteen  pounds  in  an  individual  of 
average  physical  development.  The  quantity  varies  during  the  twenty-four 
hours,  the  maximum  being  reached  in  the  afternoon,  the  minimum  in  the 
early  morning  hours. 

Blood  is  an  opaque,  red  fluid,  having  an  alkaline  reaction,  a  saline  taste, 
and  a  specific  gravity  of  1055. 

The  opacity  is  due  to  the  refraction  of  the  rays  of  light  by  the  elements 
of  which  the  blood  is  composed.  The  color  varies  in  hue,  from  a  bright 
scarlet  in  the  arteries  to  a  deep  purple  in  the  veins,  due  to  the  presence  of 
a  coloring-matter — hemoglobin — in  different  degrees  of  oxidation. 

The  alkalinity  is  constant,  and  depends  upon  the  presence  of  the  alka- 
line sodium  phosphate,  Na2HPOr 

The  saline  taste  is  due  to  the  amount  of  sodium  chlorid  present. 

Within  the  limits  of  health  the  specific  gravity  ranges  from  1045  to  1075. 

The  odor  of  the  blood  is  characteristic,  and  varies  with  the  animal  from 
which  it  is  drawn  ;  it  is  due  to  the  presence  of  caproic  acid. 

The  temperature  of  the  blood  ranges  from  9S0  F.  at  the  surface  to  1070 
F.  in  the  hepatic  vein  ;  it  loses  heat  by  radiation  and  evaporation  as  it 
approaches  the  extremities  and  as  it  passes  through  the  lungs. 

Blood  Consists  of  Two  Portions  : 

1.  The  liquor  sanguinis  ox  plasma,  a  transparent,  colorless  fluid,  in  which 
are  floating — 

2.  Red  and  white  corpuscles,  these  constituting  by   weight  less  than  one 
half  (40  per  cent. )  of  the  entire  amount  of  blood. 


120  HUMAN    PHYSIOLOGY. 

COMPOSITION   OF    PLASMA. 

Dalton. 

Water, 902.00 

Albumin, 53°° 

Paraglobulin, 22.00 

Fibrinogen, 3-00 

Fatty  matters 2.50 

Crystallizable  nitrogenous  matters, 4.00 

Other  organic  matter, 5-°° 

Mineral  salts, 8.50 

1,000.00 


Water  acts  as  a  solvent  for  the  inorganic  matters  and  holds  in  suspension 
the  corpuscular  elements. 

Albumin  is  the  nutritive  principle  of  the  blood  ;  it  is  absorbed  by  the 
tissues  to  repair  their  waste  and  is  transformed  into  the  organic  basis  char- 
acteristic of  each  structure. 

Paraglobulin  or fibrinoplastin  is  a  soft,  amorphous  substance  precipitated 
by  sodium  chlorid  in  excess,  or  by  passing  a  stream  of  carbonic  acid 
through  dilute  serum. 

Fibrinogen  also  can  be  obtained  by  strongly  diluting  the  serum  and 
passing  carbonic  acid  through  it  for  a  long  time,  when  it  is  precipitated  as 
a  viscous  deposit. 

Fatty  matter  exists  in  small  proportion,  except  in  pathologic  conditions 
and  after  the  ingestion  of  food  rich  in  oleaginous  matters  ;  it  soon  disap- 
pears, undergoing  oxidation,  generating  heat  and  force,  or  is  deposited  as 
adipose  tissue. 

Sugar  is  represented  by  glucose,  a  product  of  the  digestion  of  saccharine 
matter  and  starches  in  the  alimentary  canal  ;  glycogenic  matter  is  derived 
from  the  liver. 

The  saline  constituents  aid  the  process  of  osmosis,  give  alkalinity  to 
the  blood,  promote  the  absorption  of  carbonic  acid  from  the  tissues  into 
the  blood,  and  hold  other  substances  in  solution ;  the  most  important 
are  the  sodium  and  potassium  chlorids  and  the  calcium  and  magnesium 
phosphates. 

Excrementitious  matters  are  represented  by  carbonic  acid,  urea,  creatin, 
creatinin,  urates,  oxalates,  etc.;  they  are  absorbed  from  the  tissues  by  the 
blood  and  conveyed  to  the  excretory  organs,  lungs,  kidneys,  etc. 

Gases. — Oxygen,  nitrogen,  and  carbonic  acid  exist  in  varying  propor- 
tions. 


BLOOD. 


121 


BLOOD-CORPUSCLES. 

The  corpuscular  elements  of  the  blood  occur  under  two  distinct  forms, 
which,  from  their  color,  are  known  as  the  red  and  white  corpuscles. 

The  red  corpuscles  as  they  float  in  a  thin  layer  of  the  liquor  sanguinis 
are  of  a  pale  straw-color  ;  it  is  only  when  aggregated  in  masses  that  they 
assume  the  bright  red  color.  In  form  they  are  circular  and  biconcave ; 
they  have  an  average  diameter  of   3^00  of  an  inch. 

In  -mammals,  birds,  reptiles,  amphibia,  and  fish  the  corpuscles  vary  in 
size  and  number,  gradually  becoming  larger  and  less  numerous  as  the  scale 
of  animal  life  is  descended,  e.  g.  : 

TABLE   SHOWING   COMPARATIVE    DIAMETER    OF    RED    CORPUSCLES. 


Mammals. 

Birds. 

Reptiles. 

Amphibia. 

Fish 

Man, 

Chimpanzee, 
Orang, 
Dog, 

32(55 
34  15 
3355 
3BS3 

Eagle,       rs»T2 
Owl,          T7l63 
Sparrow,  *^ 
SwalioWj^j'jj 

Turtle,      j^'sx 
Tortoise,    j^g^ 
Lizard,      ^s 
Viper,        15V5 

Frog, 
Toad, 
Proteus, 
Siren, 

ires 

T543 

■tun 
1 

?35 

Perch, 
Carp, 
Pike, 
Eel, 

553  5 
5T?T 
JOJS5 
175  K 

Cat, 
Hog, 

4"?U4 
4530 

Pigeon,     TgV.3 
Turkey,   ^Vo 

Amphiuma, 

3C3 

Horse, 

4"B(J(J 

Goose,      I5!Bg 

Ox, 

5357 

Swan,       T^5e 

In  man  and  the  mammals  the  red  corpuscles  present  neither  a  nucleus 
nor  a  cell  wall,  and  are  universally  of  a  small  size.  They  can  be  readily 
distinguished  from  the  corpuscles  of  birds,  reptiles,  and  fish,  in  which 
animals  they  are  larger,  oval  in  shape,  and  possess  a  well-defined  nucleus. 

The  red  corpuscles  are  exceedingly  numerous,  amounting  to  about 
5,000,000  in  a  cubic  millimeter  of  blood.  In  structure  they  consist  of  a 
firm,  elastic,  colorless  framework, — the  stroma, — in  the  meshes  of  which 
is  entangled  the  coloring-matter — the  hemoglobin. 


CHEMIC   COMPOSITION    OF   RED    CORPUSCLES. 

Water,        68S.00 

Globulin, 282.22 

Hemoglobin, ....  16.75 

Fatty  matter,     ...                              .......  2. 3 1 

Extractives, 2.60 

Mineral  salts,    , 5.12 

1,000.00 

Hemoglobin,   the  coloring    matter  of  the  corpuscles,  is  an  albuminous 
compound,  composed  of  C,  O,  H,  N,  S,  and  iron.     It  may  exist  in  either 
an  amorphous  or  a  crystalline  form.      When  deprived  of  all  its  oxygen,  ex- 
cept the  quantity  entering  into  its  intimate  composition,  the  hemoglobin 
9 


122  HUMAN   PHYSIOLOGY. 

becomes  purplish  in  color,  and  is  known  as  reduced  hemoglobin.  When 
exposed  to  the  action  of  oxygen,  it  again  absorbs  a  definite  amount  and 
becomes  scarlet  in  color,  and  is  known  as  oxyhemoglobin.  The  amount  of 
oxygen  absorbed  is  1. 76  c. c.  (y^of  a  cubic  inch)  for  I  mg.  (^  of  a 
grain)  of  hemoglobin. 

It  is  this  substance  which  gives  the  color  to  the  venous  and  arterial 
blood.  As  the  venous  blood  passes  through  the  capillaries  of  the  lungs 
the  reduced  hemoglobin  absorbs  the  oxygen  from  the  pulmonary  air  and 
becomes  oxyhemoglobin,  scarlet  in  color  ;  the  blood  becomes  arterial. 
When  the  arterial  blood  passes  into  the  systemic  capillaries,  the  oxygen  is 
absorbed  by  the  tissues  ;  the  hemoglobin  becomes  reduced,  purple  in  color, 
and  the  blood  becomes  venous.  A  dilute  solution  of  oxyhemoglobin  gives 
two  absorption  bands  between  the  lines  D  and  E  of  the  solar  spectrum. 
Reduced  hemoglobin  gives  but  one  absorption  band,  occupying  the  space 
existing  between  the  two  bands  of  the  oxyhemoglobin  spectrum. 

The  function  of  the  red  corpuscle  is,  therefore,  to  absorb  oxygen  and 
carry  it  to  the  tissues  ;  the  smaller  the  corpuscles  and  the  greater  the  num- 
ber, the  greater  is  the  quantity  of  oxygen  absorbed,  and,  consequently,  all 
the  vital  functions  of  the  body  become  more  active. 

The  white  corpuscles  are  far  less  numerous  than  the  red,  the  proportion 
being,  on  an  average,  about  I  white  to  from  350  to  400  red  ;  they  are 
globular  in  shape,  and  are  ^Vc  °^  an  incn  m  diameter,  and  consist  of  a 
soft,  granular,  colorless  substance,  containing  several  nuclei. 

The  white  corpuscles  possess  the  power  of  spontaneous  movement,  alter- 
nately contracting  and  expanding,  throwing  out  processes  of  their  substance 
and  quickly  withdrawing  them,  thus  changing  their  shape  from  moment  to 
moment.  These  movements  resemble  those  of  the  ameba,  and  for  this 
reason  are  termed  ameboid.  The  white  corpuscles  also  possess  the  capa- 
bility of  moving  from  place  to  place.  In  the  interior  of  the  vessels  they 
adhere  to  the  inner  surface,  while  the  red  corpuscles  move  through  the 
center  of  the  stream. 

The  white  corpuscles  are  identical  with  the  leukocytes,  and  are  found  in 
milk,  lymph,  chyle,  and  other  fluids. 

Origin  of  Corpuscles. — The  red  corpuscles  take  their  origin  from  the 
mesoblastic  cells  in  the  vascular  area  of  the  developing  embryo. 

In  the  adult  they  are  produced  from  colorless,  nucleated  corpuscles  re- 
sembling the  white  corpuscles.  The  spleen  is  the  organ  in  which  they  are 
finally  destroyed. 

The  white  corpuscles  originate  from  the  leukocytes  of  the  adenoid  tissue, 


BLOOD.  123 

and  subsequently  give  rise  to  the  red  corpuscles  ;    they  assist  in  the  forma- 
tion of  the  new  tissues  that  result  from  inflammatory  action. 


COAGULATION  OF  THE  BLOOD. 

When  blood  is  withdrawn  from  the  body  and  allowed  to  remain  at  rest, 
it  becomes  somewhat  thick  and  viscid  in  from  three  to  five  minutes  ;  this 
viscidity  gradually  increases  until  the  entire  volume  of  blood  assumes  a 
jelly- like  consistence,  which  process  occupies  from  five  to  fifteen  minutes. 

As  soon  as  coagulation  is  completed,  a  second  process  begins,  which 
consists  in  the  contraction  of  the  coagulum  and  the  oozing  of  a  clear, 
straw-colored  liquid,  —  the  serum,  — which  gradually  increases  in  quantity 
as  the  clot  diminishes  in  size,  by  contraction,  until  the  separation  is  com- 
pleted, which  occupies  from  twelve  to  twenty-four  hours. 

The  changes  in  the  blood  are  as  follows  : 

Before  coagulation. 

{Liq.  Sanguinis,  ~\  C  Water. 

>  consisting  of  J  Albumin. 
J  )  Fibrinogen. 

Plasma,  v.  Salts. 

Corpuscles,  red  and  white. 
After  coagulation. 

{Crassamentum,  >  .   .  f  Fibrin. 

Clot  or  coagulum,  J  I  Corpuscles, 

r  Water. 
Serum,  containing       -J  Albumin. 

I  Salts. 

The  serum,  therefore,  differs  from  the  liquor  sanguinis  in  not  containing 
fibrin. 

In  from  twelve  to  twenty-four  hours  the  upper  surface  of  the  clot 
presents  a  grayish  appearance,  —  the  buffy  coat,  —  owing  to  the  rapid  sink- 
ing of  the  red  corpuscles  beneath  the  surface,  permitting  the  fibrin  to  coagu- 
late without  them  ;  this  substance  then  assumes  a  grayish-yellow  tint.  In- 
asmuch as  the  white  corpuscles  possess  a  lighter  specific  gravity  than  the 
red,  they  do  not  sink  so  rapidly,  and,  becoming  entangled  in  the  fibrin, 
assist  in  forming  the  buffy  coat.  Continued  contraction  gives  a  cupped 
appearance  to  the  surface  of  the  clot. 

Inflammatory  states  of  the  blood  produce  a  marked  increase  in  the  buffed 
and  cupped  condition,  on  account  of  the  aggregation  of  the  corpuscles 
and  their  tendency  to  rapid  sinking. 


124  HUMAN   PHYSIOLOGY. 

Nature  of  Coagulation.  —  Coagulated  fibrin  does  not  preexist  in  the 
blood,  but  is  formed  at  the  moment  blood  is  withdrawn  from  the  vessels. 
According  to  Denis,  a  liquid  substance — plasmin — exists  in  the  blood, 
which,  when  withdrawn  from  the  circulation,  decomposes  into  fibrin  and 
metalbnmin. 

According  to  Schmidt,  fibrin  results  from  the  union  of  fibrinoplastin 
(paraglobulin)  and  fibrinogen,  brought  about  by  the  presence  of  a  third 
substance,  the  fibrin-ferment. 

According  to  Hammersten  and  others,  the  fibrin  obtained  from  the  blood 
after  coagulation  comes  from  the  fibrinogen  alone,  the  conversion  being 
brought  about  by  the  presence  of  a  ferment  substance,  paraglobulin  in  this 
case  having  nothing  to  do  with  the  change.  This  view  is  supported  by  the 
fact  that  the  quantity  of  fibrin  obtained  from  the  blood  is  never  greater  than 
the  quantity  of  fibrinogen  previously  present.  The  origin  of  the  ferment  is 
obscure,  but  there  is  reason  to  believe  that  it  comes  from  the  injured  vascu- 
lar coats  or  from  the  breaking  of  the  white  corpuscles. 

Conditions  Influencing  Coagulation.  —  The  process  is  retarded  by 
cold,  retention  within  living  vessels,  neutral  salts  in  excess,  inflammatory 
conditions  of  the  system,  imperfect  aeration,  exclusion  from  air,  etc. 

It  is  accelerated  by  a  temperature  of  ioo°  F.,  contact  with  air,  rough 
surfaces,  and  rest. 

Blood  coagulates  in  the  body  after  the  arrest  of  the  circulation  in  the 
course  of  twelve  to  twenty-four  hours  ;  local  arrest  of  the  circulation,  from 
compression  or  a  ligature,  will  cause  coagulation,  thus  preventing  hemor- 
rhages from  wounded  vessels. 

The  composition  of  the  blood  varies  in  different  portions  of  the  body. 
The  arterial  differs  from  the  venous,  in  being  more  coagulable  ;  in  contain- 
ing more  oxygen  and  less  carbonic  acid  ;  in  having  a  bright  scarlet  color, 
from  the  union  of  oxygen  with  hemoglobin.  The  purple  hue  of  venous 
blood  results  from  the  deoxidation  of  the  coloring-matter. 

The  blood  of  the  portal  vein  differs  in  constitution,  according  to  different 
stages  of  the  digestive  process  ;  during  digestion  it  is  richer  in  water,  albu- 
minous matter,  and  sugar ;  occasionally  it  contains  fat ;  corpuscles  are 
diminished,  and  there  is  an  absence  of  biliary  substances. 

The  blood  of  the  hepatic  vein  contains  a  larger  proportion  of  red  and 
white  corpuscles ;  the  sugar  is  augmented,  while  albumin,  fat,  and  fibrin 
are  diminished. 


CIRCULATION   OF   THE   BLOOD.  125 


CIRCULATION   OF  THE   BLOOD. 

The  circulatory  apparatus  by  which  the  blood  is  distributed  to  all 
portions  of  the  body  consists  of  a  central  organ, — the  heart, — with  which 
is  connected  a  system  of  closed  vessels  known  as  arteries,  capillaries,  and 
veins.  Within  this  system  the  blood  is  kept,  by  the  action  of  the  heart,  in 
continual  movement,  distributing  nutritive  matter  to  all  portions  of  the 
body  and  carrying  waste  matters  from  the  tissues  to  the  various  eliminating 
organs. 

The  heart  is  a  hollow,  muscular  organ,  pyramidal  in  shape,  measuring 
about  $}4  inches  in  length  and  about  3j4  in  breadth,  weighing  from  10  to 
12  ounces  in  the  male  and  from  8  to  io  in  the  female.  Situated  in  the 
thoracic  cavity,  between  the  lungs,  its  base  is  directed  upward,  backward, 
and  to  the  right ;  its  apex  is  directed  downward  and  to  the  left. 

Pericardium. — The  heart  is  surrounded  by  a  closed  fibrous  membrane 
called  the  pericardium.  The  inner  surface  of  this  membrane  is  lined  by  a 
serous  membrane,  which  is  also  reflected  over  the  surface  of  the  heart ; 
between  the  two  surfaces  of  the  serous  membrane  is  found  a  small  quantity 
of  fluid  (the  pericardial  fluid),  which  lubricates  the  surfaces  and  prevents 
friction  during  the  movements  of  the  heart.  The  interior  of  the  heart  is 
also  lined  by  a  serous  membrane,  called  the  endocardium. 

Cavities  of  the  Heart. — The  general  cavity  of  the  heart  is  subdivided 
by  a  longitudinal  septum  into  a  right  and  left  half;  each  of  these  cavities 
is  in  turn  subdivided  by  a  transverse  constriction  into  two  smaller  cavities, 
which  communicate  with  each  other  and  are  known  as  the  auricles  and 
ventricles,  the  orifice  between  the  auricle  and  ventricle  being  known  as  the 
auriculoventricular  orifice.  The  heart,  therefore,  consists  of  four  cavities 
— a  right  auricle  and  ventricle  and  a  left  auricle  and  ventricle. 

Into  the  right  auricle  the  two  terminal  trunks  of  the  venous  system — the 
superior  and  inferior  vence  cava: — empty  the  venous  blood  which  has  been 
collected  from  all  parts  of  the  system ;  from  the  right  ventricle  arises  the 
pulmonary  artery,  which,  passing  into  the  lungs,  distributes  the  blood  to 
the  walls  of  the  air-cells  of  the  lungs  ;  into  the  left  auricle  empty  four 
pulmonary  veins,  which  have  collected  the  blood  from  the  lung  capil- 
laries ;  from  the  left  ventricle  springs  the  aorta,  the  general  trunk  of  the 
arterial  system,  the  branches  of  wh'ch  distribute  the  blood  to  the  entire 
system. 


126 


HUMAN    PHYSIOLOGY. 


Fig.  17.  —  Scheme  of  the  Cir- 
culation.— {Landois.) 

a  Right,  b.  left,  auricle.  A.  Right, 
B,  left  ventricle.  1.  Pulmon- 
ary artery.  2.  Aorta.  1.  Area 
of  pulmonary,  K,  area  of  sys- 
temic, circulation.  o.  The 
superior  vena  cava.  G  Area 
supplying  the  inferior  vena 
cava,  u.  d,  d.  Intestine,  m. 
Mesenteric  artery,  q.  Portal 
vein.  L.  Liver,  h.  Hepatic 
vein. 


The  Valves  of  the  Heart.— The 
valves  of  the  heart  are  formed  by  a  redup- 
lication of  the  endocardium  strengthened 
by  connective  tissue.  At  the  auriculo- 
ventricular  openings  on  the  right  and 
left  sides  of  the  heart,  respectively,  are 
found  the  tricuspid  and  mitral  valves. 
The  tricuspid  valve  consists  of  three,  the 
mitral  of  two,  cusps  or  segments,  which 
project  into  the  interior  of  the  ventricle 
when  it  does  not  contain  blood.  At  their 
bases  the  segments  are  united  so  as  to 
form  an  annular  membrane  attached  to 
the  margin  of  the  orifice.  To  the  free 
edges  of  the  valves  are  attached  numer- 
ous fine  threads, — the  chorda  tendinece, — 
which  are  the  tendons  of  the  small  papil- 
lary muscles  springing  from  the  walls  of 
the  ventricles. 

The  Semilunar  Valves. — At  the  open- 
ings of  the  pulmonary  artery  and  the 
aorta  are  found  three  cup  shaped  or  sem- 
ilunar valves,  the  free  edges  of  which  are 
directed  away  from  the  interior  of  the 
heart.  The  anatomic  arrangement  of  the 
valves  is  such  that  upon  their  closure 
regurgitation  of  the  blood  is  prevented. 


The  Course  of  the  Blood  through 
the  Heart. — Reference  to  figure  17  will 
make  it  clear  that  there  is  a  pathway  for 
the  blood  between  the  venae  cavae  on  the 
right  side  and  the  aorta  on  the  left  side 
by  way  of  the  right  side  of  the  heart,  the 
cardio-pulmonary  vessels  and  the  left  side 
of  the  heart. 

The  venous  blood  flowing  towards  the  heart  is  emptied  by  the  superior  and 
inferior  venae  cavae  into  the  right  auricle  from  which  it  passes  through  the 
auriculoventricular  opening  into  the  right  ventricle  ;  thence  into  and  through 
the  pulmonary  artery  and  its  branches  to  the  pulmonary  capillaries  where  it 


CIRCULATION    OF   THE    BLOOD.  127 

is  arterialized,  i.  e.,  yields  up  its  carbon  dioxid  and  takes  on  a  fresh  supply 
of  oxygen — and  is  changed  in  color  from  dark  blue  to  scarlet  red.  The 
arterialized  blood  flowing  towards  the  heart  is  emptied  by  the  pulmonary 
veins  into  the  left  auricle  from  which  it  passes  through  the  auriculoventric- 
ular  opening  into  the  left  ventricle  ;  thence  into  the  aorta  and  its  branches 
to  the  systemic  capillaries  where  it  is  de-arterialized  by  an  opposite  exchange 
of  gases,  i.  e.,  yields  up  a  portion  of  its  oxygen  to,  and  absorbs  carbon 
dioxid  from  the  tissues,  and  changes  in  color  from  scarlet  to  dark  blue.  The 
venous  blood  is  again  returned  by  the  systemic  veins  to  the  venae  cavae. 

While  there  is  but  one  circulation,  physiologists  frequently  divide  the 
circulatory  apparatus  into — 

1 .  The  systemic  circulation,  which  includes  the  movement  of  the  blood  from 
the  left  side  of  the  heart  through  the  aorta  and  its  branches,  through  the 
capillaries  and  veins,  to  the  right  side. 

2.  The  pulmonary  circulation,  which  includes  the  course  of  the  blood  from 
the  right  side  through  the  pulmonary  artery,  through  the  capillaries  of 
the  lungs  and  pulmonary  veins,  to  the  left  side  of  the  heart. 

3.  The  portal  circulation,  which  includes  the  portal  vein.  This  vein  is 
formed  by  the  union  of  the  radicles  of  the  gastric,  mesenteric,  and  splenic 
veins,  and  carries  the  blood  directly  into  the  liver,  where  the  vein  divides 
into  a  fine  capillary  plexus,  from  which  the  hepatic  veins  arise  ;  these 
empty  into  the  ascending  vena  cava. 

The  Mechanism  of  the  Heart. — The  immediate  cause  of  the  move- 
ment of  the  blood  through  the  blood-vessels  is  the  alternate  contraction 
and  relaxation  of  the  muscular  walls  of  the  heart,  and  more  especially  the 
walls  of  the  ventricles,  each  of  which  plays  alternately  the  part  of  a  force 
pump  and  to  a  slight  extent  of  a  suction  pump.  The  motive  power  is  fur- 
nished by  the  heart  itself.  The  contraction  of  any  part  of  the  heart  is  termed 
the  systole,  the  relaxation,  the  diastole ;  as  each  side  of  the  heart  has  two 
cavities,  the  walls  of  which  contract  and  relax  in  succession,  it  is  customary 
to  speak  of  an  auricular  systole  and  diastole  and  a  ventricular  systole  and 
diastole  ;  as  the  two  sides  are  in  the  same  physiologic  relation  they  contract 
and  relax  in  the  same  periods  of  time. 

Movements  of  the  Heart.  —  At  each  beat,  during  the  systole, 
the  heart  hardens  and  becomes  shortened  in  its  long  diameter  ;  its  apex  is 
raised  up,  rotated  on  its  axis  from  left  to  right,  and  thrown  forward  against 
the  walls  of  the  chest.  The  impulse  of  the  heart,  observed  about  two 
inches  below  the  nipple  and  one  inch  to  the  sternal  side,  between  the  fifth 
and  sixth  ribs,  is  caused  mainly  by  the  apex  of  the  heart  striking  against 


128  HUMAN    PHYSIOLOGY. 

the  chest  walls,  assisted  by  the  distention  of  the  great  vessels  about  the  base 
of  the  heart. 

The  Cardiac  Cycle. — The  entire  period  of  the  heart's  pulsation  may  be 
divided  into  three  stages,  viz.  : 

1.  The  auricular  contraction  and  relaxation. 

2.  The  ventricular  contraction  and  relaxation. 

3.  The  pause  or  period  of  repose  during  which  both  auricles  and  ventricles 
are  at  rest.  These  three  stages  constitute  collectively  a  cardiac  cycle  or 
a  cardiac  revolution. 

L  The  duration  of  a  cycle,  as  well  as  the  duration  of  its  three  stages,  varies 
in  different  animals  in  accordance  with  the  number  of  cycles  which  recur 
in  a  minute.  In  human  beings  in  adult  life  there  are  about  72  cycles  to 
the  minute;  the  average  duration  is,  therefore,  0.80  sec.  From  this  it 
follows  that  the  time  occupied  by  any  one  of  the  three  stages  must  be 
extremely  short  and  difficult  of  determination.  From  experiments  on 
animals  and  from  observations  made  on  human  beings,  the  following  esti- 
mates have  been  made  and  accepted  as  approximately  correct  for  human 
beings  : 

1.  The  auricular  systole — 0.16  sec.  ;  the  auricular  diastole,  0.64  sec. 

2.  The  ventricular  systole — 0.32  sec.  ;  the  ventricular  diastole,  0.48  sec. 

3.  The  period  of  rest  for  both  auricles  and  venticles — 0.32  sec. 

The  Action  of  the  Valves. — The  forward  movement  of  the  blood  is 
permitted  and  regurgitation  prevented  by  the  alternate  action  of  the  auriculo- 
ventricular  and  semilunar  valves  as  a  point  of  departure  for  a  consideration 
of  the  action  of  these  valves  and  their  relation  to  the  systole  and  diastole 
of  the  heart,  the  close  of  the  ventricular  systole  may  be  selected.  At  this 
moment,  the  semilunar  valves,  which  during  the  systole,  are  directed 
outward  by  the  blood  current  are  now  suddenly  and  completely  closed  by 
the  pressure  of  the  blood  in  the  aorta  and  pulmonary  artery.  Regurgitation 
into  the  ventricles  is  thus  prevented. 

During  the  ventricular  systole,  the  relaxed  auricles  are  filling  with  blood. 
With  the  ventricular  diastole  this  blood  or  its  equivalent  flows  into  the 
relaxed  and  easily  distensible  ventricles  until  both  auricles  and  ventricles 
are  nearly  filled.  The  tricuspid  and  mitral  valves  which  are  hanging  down 
into  the  ventricular  cavities,  are  now  floated  up  by  currents  of  blood  welling 
up  behind  them  until  they  are  nearly  closed.  The  auricles  now  suddenly 
contract,  forcing  their  contained  volumes  into  the  ventricles  which  become 
fully  distended. 

With-the  cessation  of  the  auricular  systole,  the  ventricular  systole  begins. 


CIRCULATION   OK  THE   BLOOD.  129 

If  the  blood  is  not  to  be  returned  to  the  auricles  the  tricuspid  and  mitral 
valves  must  be  instantly  and  completely  closed.  This  is  accomplished  by 
the  upward  pressure  of  the  blood  which  brings  their  free  edges  in  close 
apposition.  Reversal  of  these  valves  is  prevented  by  the  contraction  of  the 
papillary  muscles  which  exert  a  traction  on  their  under  surfaces  and  edges 
and  hold  them  steady. 

The  blood  now  confined  in  the  ventricles  between  the  closed  auriculo- 
ventricular  and  semilunar  valves  is  subjected  to  pressure  on  all  sides  ;  as  the 
pressure  rises  proportionately  to  the  vigor  of  the  contraction  there  comes  a 
moment  when  the  intra-ventricular  pressure  exceeds  that  in  the  aorta 
and  pulmonary  artery  ;  at  once  the  semilunar  valves  are  thrown  open  and 
the  blood  discharged.  Both  contraction  and  outflow  continue  until  the 
ventricles  are  practically  empty,  when  relaxation  sets  in  attended  by  a  rapid 
fall  of  pressure,  under  the  influence  of  the  positive  pressure  of  the  blood  in 
the  aorta  and  pulmonary  artery,  the  semilunar  valves  are  again  closed.  The 
accumulation  of  blood  in  the  auricles,  attended  by  a  rise  in  pressure,  again 
•forces  the  tricuspid  and  mitral  valves  open.  With  these  events  the  cardiac 
cycle  is  again  completed. 

Sounds  of  the  Heart. — If  the  ear  be  placed  over  the  cardiac  region, 
two  distinct  sounds  are  heard  during  each  revolution  of  the  heart,  closely 
following  each  other,  and  which  differ  in  character. 

The  sound  coinciding  with  the  systole  in  point  of  time — the  first  sound — 
is  prolonged  and  dull,  and  caused  by  the  closure  and  vibration  of  the  auricu- 
loventricular  valves,  the  contraction  of  the  walls  of  the  ventricles,  and  the 
apex-beat ;  the  second  sound,  occurring  during  the  diastole,  is  short  and 
sharp,  and  caused  by  the  closure  of  the  semilunar  valves. 

The  frequency  of  the  heart's  action  varies  at  different  periods  of  life, 
but  in  the  adult  male  it  beats  about  seventy-two  times  a  minute.  It  is 
influenced  by  age,  exercise,  posture,  digestion,  etc. 

Age. — Before  birth,  the  number  of  pulsations  a  minute  averages       .    .  140 

During  the  first  year  it  diminishes  to 128 

During  the  third  year  diminishes  to      .  95 

From  the  eighth  to  the  fourteenth  year  averages 84 

In  adult  life  the  average  is .    .    .    .    72 

Exercise  and  digestion  increase  the  frequency  of  the  heart's  action. 

Posture  influences  the  number  of  pulsations  a  minute  ;  in  the  male, 
standing,  the  average  is  81  ;  sitting,  71  ;  lying,  66 — independent,  for  the 
most  part,  of  muscular  effort. 

The  rhythmic  movements  of  the  heart  are  dependent  upon — 


130  HUMAN    PHYSIOLOGY. 

1.  An  inherent  irritability  of  the  muscle-fiber,  which  manifests   itself  as 
long  as  the  nutrition  is  maintained. 

2.  The  continuous  flow  of  blood  through  its  cavities,  distending  them  and 
stimulating  the  endocardium. 

The  force  exerted  by  the  left  ventricle  at  each  contraction  has  been 
estimated  at  fifty-two  pounds.  If  a  tube  be  inserted  into  the  aorta,  the 
pressure  there  will  be  sufficient  to  support  a  column  of  blood  nine  feet,  or 
a  column  of  mercury  six  inches,  in  height,  the  weight  in  either  case  being 
about  four  pounds.  The  estimation  of  the  force  which  the  heart  is  required 
to  exert  to  support  this  column  of  blood  is  arrived  at  by  multiplying  the 
pressure  in  the  aorta  (four  pounds)  by  the  area  of  the  internal  surface  of 
the  left  ventricle  (about  thirteen  inches),  each  inch  of  the  ventricle  being 
capable  of  supporting  a  downward  pressure  of  four  pounds. 

Work  Done  by  the  Heart.  —The  work  done  by  the  heart  is  estimated 
by  multiplying  the  amount  of  blood  sent  out  from  the  right  and  left  ven- 
tricles at  each  contraction  by  the  pressure  of  the  pulmonary  artery  and 
aorta,  respectively — e.  g.,  when  the  right  ventricle  contracts,  it  forces  out 
^  of  a  pound  of  blood,  and  in  so  doing  must  overcome  a  pressure  in  the 
pulmonary  artery  sufficient  to  support  a  column  of  blood  three  feet  in 
height ;  that  is,  must  exert  energy  sufficient  to  raise  ^  of  a  pound  3  feet, 
or  ^  X  3>  or  %  °f  a  pound  I  foot.  When  the  left  ventricle  contracts,  it 
sends  out  }(  of  a  pound  of  blood,  and  in  so  doing  the  left  ventricle  must 
overcome  a  pressure  in  the  aorta  sufficient  to  support  a  column  of  blood  9 
feet  in  height ;  that  is,  must  exert  energy  sufficient  to  raise  %  of  a  pound 
9  feet,  or  ^  X  9>  or  2X  pounds  I  foot.  Work  done  is  estimated  by  the 
amount  of  energy  required  to  raise  a  definite  weight  a  definite  height  ;  the 
unit,  the  foot-pound,  being  that  required  to  raise  I  pound  I  foot. 

The  heart,  therefore,  at  each  systole  exerts  energy  sufficient  to  raise  3 
foot-pounds,  and  as  it  contracts  72  times  a  minute,  it  would  raise  in  that 
time  3  X  72j  or  2I6  foot-pounds;  and  in  one  hour  216X60,  or  12,960 
foot-pounds;  and  in  twenty-four  hours  12,960  X  24>  or  3ll>°4°  foot- 
pounds, or  138.5  foot-tons. 

Influence  of  the  Nervous  System  upon  the  Heart. — When  the 
heart  of  a  frog  is  removed  from  the  body,  it  continues  to  beat  for  a  variable 
length  of  time,  depending  upon  the  nature  of  the  conditions  surrounding 
it.  The  heart  of  a  warm-blooded  animal  continues  to  beat  but  for  a  very 
short  time.  The  cause  of  the  continued  pulsations  of  the  frog-heart  is  the 
presence  of  nerve-ganglia  in  its  substance.     These  ganglia^  have  riot  been 


CIRCULATION    OF   THE   BLOOD.  131 

shown  to  exist  in  the  mammalian  heart,  but  there  is  reason  to  believe  that 
the  nervous  mechanism  is  fundamentally  the  same. 

The  ganglia  of  the  heart  are  three  in  number  :  one  situated  at  the  open- 
ing of  the  inferior  vena  cava  (the  ganglion  of  Remak),  a  second  situated 
in  the  auriculoventricular  septum  (the  ganglion  of  Biddle),  and  a  third 
situated  in  the  interauricular  septum  (the  ganglion  of  Ludwig).  The  first 
two  are  motor  in  function  and  excite  the  pulsations  of  the  heart ;  the  third 
is  inhibitory  in  function  and  retards  the  action  of  the  heart.  The  actions 
of  these  ganglia,  though  for  the  most  part  automatic,  are  modified  by  impres- 
sions coming  through  nerves  from  the  medulla  oblongata.  When  the 
inhibitory  center  is  stimulated  by  muscarin,  the  heart  is  arrested  in  dias- 
tole ;  when  atropin  is  applied,  the  heart  recommences  to  beat,  because 
atropin  paralyzes  the  inhibitory  center. 

The  nerves  modifying  the  action  of  the  heart  are  the  pneumogastric 
(vagus)  and  the  accelerator  nerves. 

The  pneumogastric  nerve,  after  emerging  from  the  medulla,  receives 
motor  fibers  from  the  spinal  accessory  nerve.  It  then  passes  downward, 
giving  off  branches,  some  of  which  terminate  in  the  inhibitory  ganglion. 
Stimulation  of  the  vagus,  by  increasing  the  activity  of  the  inhibitory  center, 
arrests  the  heart  in  diastole  with  its  cavities  full  of  blood  ;  but  as  the  stim- 
ulation is  only  temporary,  after  a  few  seconds  the  heart  recommences  to 
beat ;  at  first  the  pulsations  are  weak  and  feeble,  but  they  soon  regain  their 
original  vigor.  After  the  administration  of  atropin  in  sufficient  doses  to 
destroy  the  termination  of  the  pneumogastric,  stimulation  of  its  trunk  has 
no  effect  upon  the  heart'.  The  inhibitory  fibers  in  the  vagus  are  constantly 
in  action,  for  division  of  the  nerve  on  both  sides  is  always  followed  by  an 
increase  in  the  frequency  of  the  heart's  pulsations. 

The  accelerator  fibers  arise  in  the  medulla,  pass  down  the  cord,  emerge 
in  the  cervical  region,  pass  to  the  last  cervical  and  first  dorsal  ganglia  of 
the  sympathetic,  and  thence  to  the  heart.  Stimulation  of  these  fibers 
causes  an  increased  frequency  of  the  heart's  pulsations,  but  they  are  dimin- 
ished in  force. 

ARTERIES. 

The  arteries  are  a  series  of  branching  tubes  conveying  blood  to  all 
portions  of  the  body.     They  are  composed  of  three  coats  : 

1.  External,  formed  of  areolar  and  elastic  tissue. 

2.  Middle,  contains  both  elastic  and  muscle  fibers,  arranged  transversely 
to  the  long  axis  of  the  artery.  The  elastic  tissue  is  more  abundant  in 
the  larger  vessels,  the  muscular  in  the  smaller. 


132  HUMAN   PHYSIOLOGY. 

3.   Internal,  composed  of  a  thin,  homogeneous  membrane,  covered  with  a 

layer  of  elongated  endothelial  cells. 

The  arteries  possess  both  elasticity  and  contractility. 

The  property  of  elasticity  allows  the  arteries  already  full  to  accommodate 
themselves  to  the  incoming  amount  of  blood,  and  to  convert  the  intermit- 
tent acceleration  of  blood  in  the  large  vessels  into  a  steady  and  continuous 
stream  in  the  capillaries. 

The  contractility  of  the  smaller  vessels  equalizes  the  current  of  blood, 
regulates  the  amount  going  to  each  part,  and  promotes  the  onward  flow  of 
blood. 

Blood-pressure. — Under  the  influence  of  the  ventricular  systole,  the 
recoil  of  the  elastic  walls  of  the  arteries,  and  the  resistance  offered  by  the 
capillaries,  the  blood  is  constantly  being  subjected  to  a  certain  amount  of 
pressure.  If  a  large  artery  of  an  animal  be  divided,  and  a  glass  tube  of 
the  same  caliber  be  inserted  into  its  lumen,  the  blood  will  rise  to  a  height 
of  about  nine  feet ;  or  if  it  be  connected  with  a  mercurial  manometer,  the 
mercury  will  rise  to  a  height  of  six  inches.  This  height  will  be  a  measure, 
of  the  pressure  in  the  vessel.  The  absolute  quantity  of  mercury  sustained 
by  an  artery  can  be  ascertained  by  multiplying  the  height  of  the  column 
by  the  area  of  a  transverse  section  of  that  artery. 

The  pressure  of  the  blood  is  greatest  in  the  large  arteries,  but  gradually 
decreases  toward  the  capillaries. 

The  blood-pressure  is  increased  or  diminished  by  influences  acting  upon 
the  heart  or  upon  the  peripheral  resistance  of  the  capillaries,  viz. : 

If,  while  the  force  of  the  heart  remains  the  same,  the  number  of  pulsa- 
tions a  minute  increases,  thus  increasing  the  volume  of  blood  in  the  arteries, 
the  pressure  rises.  If  the  rate  remains  the  same,  but  the  force  increases, 
the  pressure  again  rises.  Causes  that  increase  the  peripheral  resistance 
by  contracting  the  arterioles — e.  g.,  irritation  of  the  vasomotor  nerves,  cold, 
etc. — produce  an  increase  of  the  pressure. 

On  the  other  hand,  influences  which  diminish  either  the  volume  of  the 
blood,  or  the  number  of  pulsations,  or  the  force  of  the  heart,  or  the  pe- 
ripheral resistance,  lower  the  pressure. 

The  pulse  is  the  sudden  distention  of  the  artery  in  a  transverse  and 
longitudinal  direction,  due  to  the  injection  of  a  volume  of  blood  into  the 
arteries  at  the  time  of  the  ventricular  systole.  As  the  vessels  are  already 
full  of  blood,  they  must  expand  in  order  to  accommodate  themselves  to  the 
incoming  volume  of  blood.  The  blood-pressure  is  thus  increased,  and  the 
pressure  originating  at  the  ventricle  excites  a  pulse-wave,  which  passes  from 


CIRCULATION   OF   THE  BLOOD.  133 

the  heart  toward  the  capillaries   at  the  rate  of  about  twenty-nine  feet  a 
second.      It  is  this  wave  that  is  recognized  by  the  finger. 

The  velocity  with  which  the  blood  flows  in  the  arteries  diminishes  from 
the  heart  to  the  capillaries,  owing  to  an  enlargement  in  the  united  sectional 
area  of  the  vessels  ;  the  velocity  increases  from  the  capillaries  toward  the 
heart.  The  blood  moves  most  rapidly  in  the  large  vessels,  and  especially 
under  the  influence  of  the  ventricular  systole.  From  experiments  on  animals, 
it  has  been  estimated  to  move  in  the  carotid  of  man  at  the  rate  of  sixteen 
inches  a  second,  and  in  the  large  veins  at  the  rate  of  four  inches  a  second. 

The  caliber  of  the  blood-vessels  is  regulated  by  the  vasomotor 
nerves,  which  have  their  origin  in  the  gray  matter  of  the  medulla  oblongata. 
They  issue  from  the  spinal  cord  through  the  anterior  roots  of  spinal  nerves, 
pass  through  the  sympathetic  ganglia,  and  ultimately  are  distributed  to  the 
coats  of  the  blood-vessels.  They  exert  at  different  times  a  constricting  and 
a  dilating  action  upon  the  vessels,  thus  keeping  up  the  arterial  tonus. 

Capillaries. — The  capillaries  constitute  a  network  of  vessels  of  micro- 
scopic size,  which  distribute  the  blood  to  the  inmost  recesses  of  the  tissues, 
inosculating  with  the  arteries  on  the  one  hand  and  the  veins  on  the  other ; 
they  branch  and  communicate  in  every  possible  direction. 

The  diameter  of  a  capillary  vessel  varies  from  -$-50^  to  j-^q ^  of  an  inch  ; 
the  walls  of  these  consist  of  a  delicate,  homogeneous  membrane,  ^oiyoo  °f 
an  inch  in  thickness,  lined  by  flattened,  elongated,  endothelial  cells,  be- 
tween which,  here  and  there,  are  observed  stomata. 

It  is  through  the  agency  of  the  capillary  vessels  that  the  phenomena  of 
nutrition  and  secretion  take  place,  for  here  the  blood  flows  in  an  equable 
and  continuous  current,  and  is  brought  into  intimate  relationship  with  the 
tissues — two  of  the  essential  conditions  for  proper  nutrition. 

The  rate  of  movement  in  the  capillary  vessels  is  estimated  at  one  inch  in 
thirty  seconds. 

In  the  capillary  current  the  red  corpuscles  may  be  seen  hurrying  down 
the  center  of  the  stream,  while  the  white  corpuscles  in  the  still  layer  adhere 
to  the  walls  of  the  vessel,  and  at  times  can  be  seen  to  pass  through  the 
walls  of  the  vessel  by  ameboid  movements. 

The  passage  of  the  blood  through  the  capillaries  is  mainly  due  to  the 
force  of  the  ventricular  systole  and  the  elasticity  of  the  arteries  ;  but  it  is 
probably  also  aided  by  a  power  resident  in  the  capillaries  themselves,  the 
result  of  a  vital  relation  between  the  blood  and  the  tissues. 

The  veins  are  the  vessels  which  return  the  blood  to  the  heart ;  they 


134  HUMAN    PHYSIOLOGY. 

have  their  origin  in  the  venous  radicles,  and  as  they  approach  the  heart 
converge  to  form  larger  trunks,  and  terminate  finally  in  the  venae  cavae. 
They  possess  three  coats — 

1.  External,  made  up  of  areolar  tissue. 

2.  Middle,  composed  of  non -striated  muscle -fibers  ;    yellow,   elastic,   and 
fibrous  tissue. 

3.  Internal,  an  endothelial  membrane  similar  to  that  of  the  arteries. 
Veins  are  distinguished   by  the    possession  of  valves  throughout  their 

course,  which  are  arranged  in  pairs,  and  formed  by  a  reflection  of  the  in- 
ternal coat,  strengthened  by  fibrous  tissues  ;  they  always  look  toward  the 
heart,  and  when  closed  prevent  a  reflux  of  blood  in  the  veins.  Valves  are 
most  numerous  in  the  veins  of  the  extremities,  but  are  entirely  absent  in 
many  others. 

The  onward  flow  of  blood  in  the  veins  is  mainly  due  to  the  action 
of  the  heart,  but  is  assisted  by  the  contraction  of  the  voluntary  muscles  and 
the  force  of  respiration. 

Muscular  contraction,  which  is  intermittent,  aids  the  flow  of  blood  in  the 
veins  by  compressing  them.  As  regurgitation  is  prevented  by  the  closure 
of  the  valves,  the  blood  is  forced  onward  toward  the  heart. 

Rhythmic  movements  of  veins  have  been  observed  in  some  of  the  lower 
animals,  aiding  the  onward  current  of  blood. 

During  the  movement  of  inspiration  the  thorax  is  enlarged  in  all  its 
diameters,  and  the  pressure  on  its  contents  at  once  diminishes.  Under 
these  circumstances  a  suction  force  is  exerted  upon  the  great  venous  trunks, 
which  causes  the  blood  to  flow  with  increased  rapidity  and  volume  toward 
the  heart. 

Venous  Pressure. — As  the  force  of  the  heart-beat  is  nearly  expended 
in  driving  the  blood  through  the  capillaries,  the  pressure  in  the  venous  sys- 
tem is  not  very  marked,  not  amounting  in  the  jugular  vein  of.  a  dog  to 
more  than  ^  that  of  the  carotid  artery. 

The  time  required  for  a  complete  circulation  of  the  blood  throughout  the 
vascular  system  has  been  estimated  to  be  from  twenty  to  thirty  seconds, 
while  for  the  entire  mass  of  blood  to  pass  through  the  heart  fifty-eight 
pulsations  would  be  required,  occupying  forty-eight  seconds. 

The  forces  keeping  the  blood  in  circulation  are : 

1.  Action  of  the  heart. 

2.  Elasticity  of  the  arteries. 

3.  Capillary  force. 

4.  Contraction  of  the  voluntary  muscles  upon  the  veins. 

5.  Respiratory  movements. 


RESPIRATION.  135 

RESPIRATION. 

Respiration  is  the  function  by  which  oxygen  is  absorbed  into  the 
blood  and  carbonic  acid  exhaled.  The  assimilation  of  the  oxygen  and 
the  evolution  of  carbonic  acid  takes  place  in  the  tissues  as  a  part  of  the 
general  nutritive  process,  the  blood  and  respiratory  apparatus  constituting 
the  media  by  means  of  which  the  interchange  of  gases  is  accomplished. 

The  respiratory  apparatus  consists  of  a  larynx,  trachea,  and  lungs. 

The  larynx  is  composed  of  firm  cartilages,  united  by  ligaments  and 
muscles.  Running  anteroposteriorly  across  the  upper  opening  are  four 
ligamentous  bands, — the  two  superior  or  false  vocal  cords,  and  the  two 
inferior  or  true  vocal  cords, — formed  by  folds  of  the  mucous  membrane. 
They  are  attached  anteriorly  to  the  thyroid  cartilages  and  posteriorly  to  the 
arytenoid  cartilages,  and  are  capable  of  being  separated  by  the  contraction 
of  the  posterior  crico-arytenoid  muscles,  so  as  to  admit  the  passage  of  air 
into  and  from  the  lungs. 

The  trachea  is  a  tube  from  four  to  five  inches  in  length,  f  of  an 
inch  in  diameter,  extending  from  the  cricoid  cartilage  of  the  larynx  to 
the  third  dorsal  vertebra,  where  it  divides  into  the  right  and  left  bronchi. 
It  is  composed  of  a  series  of  cartilaginous  rings,  which  extend  about  two 
thirds  around  its  circumference,  the  posterior  third  being  occupied  by  fibrous 
tissue  and  non-striated  muscle-fibers;  which  are  capable  of  diminishing  its 
caliber. 

The  trachea  is  covered  externally  by  a  tough,  fibro-elastic  membrane, 
and  internally  by  mucous  membrane,  lined  by  columnar,  ciliated,  epithelial 
cells.  The  cilia  are  always  waving  from  within  outward.  When  the  two 
bronchi  enter  the  lungs,  they  divide  and  subdivide  into  numerous  smaller 
branches,  which  penetrate  the  lungs  in  every  direction  until  they  finally 
terminate  in  the  pulmonary  lobules. 

As  the  bronchial  tubes  become  smaller  their  walls  become  thinner ;  the 
cartilaginous  rings  disappear,  but  are  replaced  by  irregular  angular  plates 
of  cartilage  ;  when  the  tube  becomes  less  than  J^  of  an  inch  in  diameter, 
they  wholly  disappear,  and  the  fibrous  and  mucous  coats  blend,  forming 
a  delicate  elastic  membrane,  with  circular  muscle- fibers. 

The  lungs  occupy  the  cavity  of  the  thorax,  are  conic  in  shape,  of  a 
pink  color  and  a  spongy  texture.  They  are  composed  of  a  great  number  of 
distinct  lobules  (the  pulmonary  lobules),  connected  by  interlobular  con- 
nective tissue.     These  lobules  vary  in  size,  are  of  an  oblong  shape,  and 


136  HUMAN   PHYSIOLOGY. 

are  composed  of  the  ultimate  ramifications  of  the  bronchial  tubes,  within 
which  are  contained  the  air-vesicles  or  cells.  The  walls  of  the  air- vesicles, 
exceedingly  thin  and  delicate,  are  lined  internally  by  a  layer  of  tessellated 
epithelium,  externally  covered  by  elastic  fibers,  which  give  the  lungs  their 
elasticity  and  distensibility. 

The  venous  blood  is  distributed  to  the  lungs  for  aeration  by  the  pulmo- 
nary artery,  the  terminal  branches  of  which  form  a  rich  plexus  of  capillary 
vessels  surrounding  the  air-cells  ;  the  air  and  blood  are  thus  brought  into 
intimate  relationship,  being  separated  only  by  the  delicate  walls  of  the  air- 
cells  and  capillaries. 

The  thoracic  cavity,  in  which  the  respiratory  organs  are  lodged,  is  of  a 
conic  shape,  having  its  apex  directed  upward,  its  base  downward.  Its 
framework  is  formed  posteriorly  by  the  spinal  column,  anteriorly  by  the 
sternum,  and  laterally  by  the  ribs  and  costal  cartilages.  Between  and  over 
the  ribs  lie  muscles,  fascia,  and  skin,  above,  the  thorax  is  completely  closed 
by  the  structures  passing  into  it  and  by  the  cervical  fascia  and  skin  ;  below, 
it  is  closed  by  the  diaphragm.     It  is,  therefore,  an  air-tight  cavity. 

The  Pleura. — Each  lung  is  surrounded  by  a  closed  serous  membrane 
(the  pleura),  one  layer  of  which  (the  visceral}  is  reflected  over  the  lung  ; 
the  other  (the  parietal ) ,  reflected  over  the  wall  of  the  thorax;  between  the 
two  layers  is  a  small  amount  of  fluid,  which  prevents  friction  during  the 
play  of  the  lungs  in  respiration. 

Owing  to  the  elastic  tissue  which  is  present  in  the  lungs,  they  are  very 
readily  distensible,  ;  so  much  so,  indeed,  that  the  pressure  of  the  air  inside 
the  trachea  and  lungs  is  sufficient  to  distend  them  until  they  completely  fill 
all  parts  of  the  thoracic  cavity  not  occupied  by  the  heart  and  great  vessels. 
The  elastic  tissue  endows  them  not  only  with  distensibility,  but  also  with 
the  power  of  elastic  recoil,  by  which  they  are  enabled  to  accommodate 
themselves  to  all  variations  in  the  size  of  the  thoracic  cavity. 

When  the  chest- walls  recede,  the  air  within  the  lungs  expands  and  presses 
them  against  the  ribs  ;  when  the  chest-walls  contract,  the  air  being  driven 
out,  the  elastic  tissue  recoils  and  the  lungs  return  to  their  original  condi- 
tion.    The  movements  of  the  lungs  are,  therefore,  entirely  passive. 

As  the  capacity  of  the  chest  in  a  state  of  rest  is  greater  than  the  volume 
of  the  lungs  after  they  are  collapsed,  it  is  quite  evident  that  in  the  living 
condition  the  lungs  are  distended  and  in  a  state  of  elastic  tension,  which 
is  greater  or  less  in  proportion  as  the  thoracic  cavity  is  increased  or  dimin- 
ished in  size.  The  elastic  tissue,  always  on  the  stretch,  is  endeavoring  to 
pull  the  visceral  layer  of  the  pleura  away  from  the  parietal  layer,  but  is 


RESPIRATION. 


137 


antagonized  by  the  pressure  of  the  air  within  the  air-passages.  This  con- 
dition of  things  persists  as  long  as  the  thoracic  cavity  remains  air-tight ;  but 
if  an  opening  be  made  in  the  thoracic  wall,  the  pressure  of  the  external  air, 
which  was  previously  supported  by  the  practically  rigid  walls  of  the  thorax, 
now  presses  upon  the  lung  with  as  much  force  as  the  air  within  the  lung. 
The  two  pressures  being  neutralized,  there  is  nothing  to  prevent  the  elastic 
tissue  from  recoiling,  driving  the  air  out,  and  collapsing.  The  elastic  tension 
of  the  lungs  can  be  readily  measured 
in  man  after  death  by  inserting  a  man- 
ometer into  the  trachea.  Upon  opening 
the  thorax  and  allowing  the  tissue  to 
recoil,  the  air  passes  upon  the  mercury 
and  elevates  it,  the  extent  to  which  it 
is  raised  being  the  index  of  the  pres- 
sure. Hutchinson  calculated  the  pres- 
sure to  be  one  half  pound  to  the  square 
inch  of  lung  surface. 

Respiratory  Movements.  —  The 
movements  of  respiration  are  two,  and 
consist  of  an  alternate  dilatation  and 
contraction  of  the  chest,  known  as  in- 
spiration and  expiration. 

1.  Inspiration  is  an  active  process,  the 
result  of  the  expansion  of  the  thorax, 
whereby  air  is  introduced  into  the 
lungs. 

2.  Expiration  is  a  partially  passive  pro- 
cess, the  result  of  the  recoil  of  the 
elastic  walls  of  the  thorax,  and  the 
recoil  of  the  elastic  tissue  of  the 
lungs,  whereby  the  carbonic  acid  is  expelled 


Fig.  18. — Diagram  of  the  Respi- 
ratory Organs. 

The  windpipe,  leading  down  from  the 
larynx,  is  seen  to  branch  into  two 
large  bronchi,  which  subdivide 
after  they  enter  their  respective 
lungs. 


In  inspiration  the  chest  is  enlarged  by  an  increase  in  all  its  diameters  — 


1.  The  vertical  is  increased  by  the  contraction  and  descent  of  the  dia- 
phragm when  it  approximates  a  straight  line. 

2.  The   anteroposterior   and   t>ansver:e   diameters    are    increased    by  the 
elevation  and  rotation  of  the  ribs  upon  their  axes. 

In  ordinary  tranquil  inspiration  the  muscles  which  elevate  the  ribs  and 
IO 


138  HUMAN   PHYSIOLOGY. 

thrust  the  sternum  forward,  and  so  increase  the  diameters  of  the  chest,  are 
the  external  inter  costals,  running  from  above  downward  and  forward,  the 
sternal  portion  of  the  internal  intercostals,  and  the  levatores  costarum. 

In  the  extraordinary  efforts  of  inspiration  certain  auxiliary  muscles  are 
brought  into  play, — viz. ,  the  sternomastoid ',  perforates,  serratus  magnus, — 
which  increase  the  capacity  of  the  thorax  to  its  utmost  limit. 

In  expiration  the  diameters  of  the  chest  are  all  diminished — viz.  : 

1.  The  vertical,  by  the  ascent  of  the  diaphragm. 

2.  The  anteroposterior,  by  a  depression  of  the  ribs  and  sternum. 

In  ordinary  tranquil  expiration  the  diameters  of  the  thorax  are  dimin- 
ished by  the  recoil  of  the  elastic  tissue  of  the  lungs  and  the  ribs  ;  but  in 
forcible  expiration  the  muscles  which  depress  the  ribs  and  sternum,  and 
thus  further  diminish  the  diameter  of  the  chest,  are  the  internal  inlercostals, 
the  infracostals,  and  the  triangularis  sterni. 

In  the  extraordinary  efforts  of  expiration  certain  auxiliary  muscles  are 
brought  into  play, — viz.,  the  abdominal  and  sacrohimbalis  muscles, — which 
diminish  the  capacity  of  the  thorax  to  its  utmost  limit. 

Expiration  is  aided  by  the  recoil  of  the  elastic  tissue  of  the  lungs  and 
ribs  and  by  the  pressure  of  the  air. 

Movements  of  the  Glottis. — At  each  inspiration  the  rima  glottidis  is 
dilated  by  a  separation  of  the  vocal  cords,  produced  by  the  contraction  of 
the  crico-arytenoid  muscles,  so  as  freely  to  admit  the  passage  of  air  into 
the  lungs  ;  in  expiration  they  fall  passively  together,  but  do  not  interfere 
with  the  exit  of  air  from  the  chest. 

Nervous  Mechanism  of  Respiration. — The  movements  of  respira- 
tory muscles,  though  capable  of  being  modified  to  a  certain  extent  by 
efforts  of  the  will,  are  of  an  automatic  character,  and  called  forth  by  ner- 
vous impulses  emanating  from  the  medulla  oblongata.  The  respiratory 
center,  the  so-called  vital  point,  generates  the  nerve  impulses,  which,  travel- 
ing outward  through  the  phrenic  and  intercostal  nerves,  excite  contractions 
of  the  diaphragm  and  intercostal  muscles,  respectively.  This  center  is  for 
the  most  part  automatic  in  its  action,  though  it  is  capable  of  being  modi- 
fied by  impulses  reflected  to  it  through  various  sensory  nerves. 

This  center  may  be  stimulated  : 
I.   Directly,  by  the  condition  of  the  blood.     An  increase  of  carbonic  acid 
or  a  diminution  of  oxygen  in  the  blood  causes  an   acceleration  of  the 
respiratory  movements  ;    the  reverse  of  these  conditions  causes  a  dimin- 
ution of  the  respiratory  movements. 


RESPIRATION.  139 

2.  Indirectly,  by  reflex  action.  The  medulla  may  be  excited  to  action 
through  the  pneumogastric  nerve,  by  the  presence  of  carbonic  acid  in  the 
lungs  irritating  its  terminal  filaments  ;  through  the  fifth  nerve,  by  irrita- 
tion of  the  terminal  branches;  and  through  the  nerves  of  general  sensi- 
bility. In  either  case  this  center  reflects  motor  impulses  to  the  respira- 
tory muscles  through  the  phrenic,  intercostah,  inferior  laryngeal,  and 
other  nerves. 

Types  of  Respiration. — The  abdominal  type  is  most  marked  in  young 
children,  irrespective  of  sex,  the  respiratory  movements  being  effected  by 
the  diaphragm  and  abdominal  muscles. 

In  the  superior  costal  type,  exhibited  by  the  adult  female,  the  respiratory 
movements  are  more  marked  in  the  upper  part  of  the  chest,  from  the  first  to 
the  seventh  ribs,  permitting  the  uterus  to  ascend  in  the  abdomen  during 
pregnancy  without  interfering  with  respiration. 

In  the  inferior  costal  type,  manifested  by  the  male,  the  movements  are 
largely  produced  by  the  muscles  of  the  lower  portions  of  the  chest,  from 
the  seventh  rib  downward,  assisted  by  the  diaphragm. 

The  respiratory  movements  vary  according  to  age,  sleep,  and  exercise, 
being  most  frequent  in  early  life,  but  averaging  twenty  a  minute  in  adult 
life.  They  are  diminished  by  sleep  and  increased  by  exercise.  There  are 
about  four  pulsations  of  the  heart  to  each  respiratory  act. 

During  inspiration  two  sounds  are  produced  :  the  one,  heard  in  the 
thorax,  in  the  trachea,  and  larger  bronchial  tubes,  is  tubular  in  character  ; 
the  other,  heard  in  the  substance  of  the  lungs,  is  vesicular  in  character. 


AMOUNT  OF  AIR   EXCHANGED  IN  RESPIRATION,  AND  CAPACITY 

OF  LUNGS. 

The  tidal  or  breathing  volume  of  air,  that  which  passes  in  and  out  of  the 
lungs  at  each  inspiration  and  expiration,  is  estimated  at  from  twenty  to 
thirty  cubic  inches. 

The  complemental  air  is  that  amount  which  can  be  taken  into  the  lungs 
by  a  forced  inspiration,  in  addition  to  the  ordinary  tidal  volume,  and 
amounts  to  about  I  io  cubic  inches. 

The  reserve  air  is  that  which  usually  remains  in  the  chest  after  the  ordi- 
nary efforts  of  expiration,  but  which  can  be  expelled  by  forcible  expiration. 
The  volume  of  reserve  air  is  about  ioo  cubic  inches. 

The  residual  air  is  that  portion  which  remains  in  the  chest  and  cannot 
be  expelled  after  the  most  forcible  expiratory  efforts,  and  which  amounts, 
according  to  Dr.  Hutchinson,  to  about  ioo  cubic  inches. 


140  HUMAN    PHYSIOLOGY. 

The  vital  capacity  of  the  chest  indicates  the  amount  of  air  that  can 
be  forcibly  expelled  from  the  lungs  after  the  deepest  possible  inspiration, 
and  is  an  index  of  an  individual's  power  of  breathing  in  disease  and  during 
prolonged  severe  exercise.  The  combined  amount  of  the  tidal,  the  com- 
plemental,  and  the  reserve  air,  230  cubic  inches,  represents  the  vital 
capacity  of  an  individual  five  feet  seven  inches  in  height.  The  vital 
capacity  varies  chiefly  with  stature.  It  is  increased  eight  cubic  inches  for 
every  inch  in  height  above  this  standard,  and  diminishes  eight  cubic  inches 
for  each  inch  below  it. 

The  tidal  volume  of  air  is  carried  only  into  the  trachea  and  large 
bronchial  tubes  by  the  inspiratory  movements.  It  reaches  the  deeper  por- 
tions of  the  lungs  in  obedience  to  the  law  of  diffusion  of  gases,  which  is 
inversely  proportionate  to  the  square  root  of  their  densities. 

The  ciliary  action  of  the  columnar  cells  lining  the  bronchial  tubes  also 
assists  in  the  interchange  of  air  and  carbonic  acid. 

The  entire  volume  of  air  passing  in  and  out  of  the  thorax  in  twenty-four 
hours  is  subject  to  great  variation,  but  can  be  readily  estimated  from  the 
tidal  volume  and  the  number  of  respirations  a  minute.  Assuming  that  an 
individual  takes  into  the  chest  twenty  cubic  inches  at  each  inspiration,  and 
breathes  eighteen  times  a  minute,  in  twenty-four  hours  there  would  pass  in 
and  out  of  the  lungs  518,400  cubic  inches,  or  300  cubic  feet. 

Chemistry  of  Respiration. — As  the  inspired  air  undergoes  a  change 
in  composition  during  its  stay  in  the  lungs  which  renders  it  unfit  for  further 
respiration,  it  becomes  requisite,  for  the  correct  understanding  of  respira- 
tion, to  ascertain  the  composition  of  both  inspired  and  expired  air. 

Composition  of  Air. — Chemic  analysis  has  shown  that  every  100 
volumes  of  air  contain  20.81  volumes  of  oxygen,  70.19  volumes  of  nitro- 
gen, and  0.03  volume  of  carbonic  acid.  Aqueous  vapor  is  also  present, 
though  the  quantity  is  variable.  The  higher  the  temperature,  the  greater 
the  amount. 

The  changes  in  the  air  effected  by  respiration  are  : 
Loss  of  oxygen,  to  the  extent  of  five  cubic  inches  per  100  of  air,  or  one  in 

twenty. 
Gain  of  carbonic  acid,  to  the  extent  of  4.66  cubic  inches  per  100  of  air,  or 

0.93  inch  in  twenty. 
Increase  of  water- vapor  and  organic  matter. 
Elevation  of  temperature. 
Increase,  and  at  times  decrease,  of  nitrogen. 
Gain  of  ammonia. 


RESPIRATION.  141 

The  total  quantity  of  oxygen  withdrawn  from  the  air  and  consumed  by 
the  body  in  twenty-four  hours  amounts  to  fifteen  cubic  feet,  and  can  be 
readily  estimated  from  the  amount  consumed  at  each  respiration.  Assum- 
ing that  one  cubic  inch  of  oxygen  remains  in  the  lungs  at  each  respiration, 
in  one  hour  there  are  consumed  1080  cubic  inches,  and  in  twenty  four 
hours  25,920  cubic  inches,  or  fifteen  cubic  feet,  weighing  eighteen  ounces. 
To  obtain  this  quantity,  300  cubic  feet  of  air  are  necessary. 

The  quantity  of  oxygen  consumed  daily  is  subject  to  considerable  varia- 
tions. It  is  increased  by  exercise,  digestion,  and  lowered  temperature,  and 
decreased  by  the  opposite  conditions. 

The  quantity  of  carbonic  acid  exhaled  in  twenty-four  hours  varies  greatly. 
It  can  be  estimated  in  the  same  way.  Assuming  that  an  individual  exhales 
0.93  -f-  cubic  inch  at  each  respiration,  in  one  hour  there  are  eliminated  1008 
cubic  inches,  and  in  twenty-four  hours  24,192  cubic  inches,  or  fourteen 
cubic  feet,  containing  seven  ounces  of  pure  carbon. 

The  exhalation  of  carbonic  acid  is  increased  by  muscular  exercise,  nitrog- 
enous food,  tea,  coffee,  and  rice,  age,  and  by  muscular  development ;  de- 
creased by  a  lowering  of  temperature,  repose,  gin  and  brandy,  and  a  dry 
condition  of  the  air. 

As  there  is  always  more  oxygen  consumed  than  carbonic  acid  exhaled, 
and  as  oxygen  unites  with  carbon  to  form  an  equal  volume  of  carbonic  acid, 
it  is  evident  that  a  certain  quantity  of  oxygen  disappears  within  the  body.  In 
all  probability  it  unites  with  the  sulphur  hydrogen  of  the  food  to  form  water. 

The  amount  of  watery  vapor  which  passes  out  of  the  body  with  the  ex- 
pired air  is  estimated  at  from  one  to  two  pounds. 

The  organic  matter,  though  slight  in  amount,  gives  the  odor  to  the  breath. 
In  a  room  with  defective  ventilation  the  organic  matter  accumulates  and 
gives  rise  to  headache,  nausea,  drowsiness,  etc.  Long-continued  breathing 
of  such  air  produces  general  ill  health.  It  is  not  so  much  the  presence  of 
C02  in  increased  amount  as  the  presence  of  organic  matter  which  necessi- 
tates thorough  ventilation. 

Condition  of  the  Gases  in  the  Blood. 

Oxygen  is  absorbed  from  the  lungs  into  the  arterial  blood  by  the  coloring- 
matter,  hemoglobin,  with  which  it  exists  in  a  state  of  loose  combination, 
and  is  disengaged  during  the  process  of  nutrition. 

Carbonic  acid,  arising  in  the  tissues,  is  absorbed  into  the  blood  in  con- 
sequence of  its  alkalinity,  where  it  exists  in  a  state  of  simple  solution  and 
also  in  a  state  of  feeble  combination  with  the  carbonates,  soda  and  potassa, 
forming  the  bicarbonates. 


142  HUMAN    PHYSIOLOGY* 

Nitrogen  is  simply  held  in  solution  in  the  plasma. 

Exchange  of  Gases  in  the  Air-cells.  —  From  the  difference  in  ten- 
sion of  the  oxygen  in  the  air-cells  (27.44  mm  of  Hg)  and  of  the  oxygen 
in  the  venous  blood  (22  mm.  Hg),  and  from  the  difference  of  the  carbonic 
acid  tension  in  the  venous  blood  (41  mm.  Hg)  and  in  the  air-cells  (27  mm. 
Hg),  it  might  be  concluded  that  the  passage  of  the  gases  is  due  solely 
to  pressure.  The  absorption  of  oxygen,  however,  does  not  follow  abso- 
lutely the  law  of  pressure;  that  chemic  processes  are  involved  is  shown 
by  the  union  of  oxygen  with  the  hemoglobin  of  the  blood  corpuscles. 
The  exhalation  of  C02  is  also  partly  a  chemic  process,  as  it  has  been 
shown  that  the  quantity  excreted  is  greatly  increased  when  oxygen  is  simul- 
taneously absorbed.  Oxygen  not  only  favors  the  exhalation  of  loosely 
combined  C02,  but  favors  the  expulsion  of  that  which  can  be  excreted  only 
by  the  addition  of  acids  to  the  blood. 

Changes  in  the  Blood  during  Respiration. 

As  the  blood  passes  through  the  lungs  it  is  changed  in  color,  from  the 
dark  purple  of  venous  blood  to  the  bright  red  of  arterial  blood. 

The  heterogeneous  composition  of  venous  blood  is  exchanged  for  the 
uniform  composition  of  the  arterial. 

It  gains  oxygen  and  loses  carbonic  acid. 

Its  coagulability  is  increased.     Temperature  is  diminished. 

Asphyxia. — If  the  supply  of  oxygen  to  the  lungs  be  diminished  and  the 
carbonic  acid  retained  in  the  blood,  the  normal  respiratory  movements  cease 
and  the  condition  of  asphyxia  ensues,  which  soon  terminates  in  death. 

The  phenomena  of  asphyxia  are  violent  spasmodic  action  of  the  respi- 
ratory muscles  attended  by  convulsions  of  the  muscles  of  the  extremities, 
engorgement  of  the  venous  system,  lividity  of  the  skin,  abolition  of  sensi- 
bility and  reflex  action,  and  death. 

The  cause  of  death  is  a  paralysis  of  the  heart  from  overdistention  by 
blood.  The  passage  of  the  blood  through  the  capillaries  is  prevented  by 
contraction  of  the  smaller  arteries,  from  irritation  of  the  vasomotor  center. 
The  heart  is  enfeebled  by  a  want  of  oxygen  and  inhibited  in  its  action  by 
the  inhibitory  centers. 


ANIMAL    HEAT.  143 

ANIMAL  HEAT. 

The  functional  activity  of  all  the  organs  and  tissues  of  the  body  is 
attended  by  the  evolution  of  heat,  which  is  independent,  for  the  most  part, 
of  external  conditions.  Heat  is  a  necessary  condition  for  the  due  perform- 
ance of  all  vital  actions  ;  although  the  body  constantly  loses  heat  by  radia- 
tion and  evaporation,  it  possesses  the  capability  of  renewing  it  and  of  main- 
taining it  at  a  fixed  standard.  The  normal  temperattcre  of  the  body  in  the 
adult,  as  shown  by  means  of  a  delicate  thermometer  placed  in  the  axilla, 
ranges  from  97. 250  F.  to  99. 50  F.,  though  the  mean  normal  temperature 
is  estimated  by  Wunderlich  at  98  6°  F. 

The  temperature  varies  in  different  portions  of  the  body  according  to 
the  extent  to  which  oxidation  takes  place,  being  highest  in  the  muscles,  in 
the  brain,  blood,  liver,  etc. 

The  conditions  which  produce  variations  in  the  normal  temperature 
of  the  body  are  :  age,  period  of  the  day,  exercise,  food  and  drink,  climate, 
season,  and  disease. 

Age.  — At  birth  the  temperature  of  the  infant  is  about  1°  F.  above  that  of 
the  adult,  but  in  a  few  hours  falls  to  95. 50  F. ,  to  be  followed  in  the  course 
of  twenty-four  hours  by  a  rise  to  the  normal  or  a  degree  beyond.  During 
childhood  the  temperature  approaches  that  of  the  adult ;  in  aged  persons 
the  temperature  remains  about  the  same,  though  they  are  not  so  capable  of 
resisting  the  depressing  effects  of  external  cold  as  adults.  A  diurnal 
variation  of  the  temperature  occurs  from  1.8°  F.  to  3.70  F.  (Jiirgensen)  ; 
the  maximum  occurring  late  in  the  afternoon,  from  4  to  9  P.  M.  ;  the  mini- 
mum, early  in  the  morning,  from  I  to  7  A.  M. 

Exercise. — The  temperature  is  raised  from  i°  to  2°  F.  during  active 
contractions  of  the  muscular  masses,  and  is  probably  due  to  the  increased 
activity  of  chemic  changes  ;  a  rise  beyond  this  point  being  prevented  by  its 
diffusion  to  the  surface,  consequent  on  a  more  rapid  circulation,  radiation, 
more  rapid  breathing,  etc. 

Food  and  Drink.  — The  ingestion  of  a  hearty  meal  increases  the  tem- 
perature but  slightly  ;  an  absence  of  food,  as  in  starvation,  produces  a 
marked  decrease.  Alcoholic  drinks,  in  large  amounts,  in  persons  unac- 
customed to  their  use,  cause  a  depression  of  the  temperature  amounting  to 
from  1°  to  2°  F.     Tea  causes  a  slight  elevation. 

External  Temperattire.  —  Long-continued  exposure  to  cold,  especially  if 
the  body  is  at  rest,  diminishes  the  temperajture  from  1°  to  2°  F.,  while 
exposure  to  a  great  heat  slightly  increases  it. 


144  HUMAN   PHYSIOLOGY. 

Disease  frequently  causes  a  marked  variation  in  the  normal  temperature 
of  the  body,  which  rises  as  high  as  1070  F.  in  typhoid  fever  and  105 °  F. 
in  pneumonia  ;  in  cholera  it  falls  as  low  as  8o°  F.  Death  usually  occurs 
when  the  heat  remains  high  and  persistent,  from  1060  to  HO°  F. ;  the  in- 
crease of  heat  in  disease  is  due  to  excessive  production  rather  than  to 
diminished  elimination. 

The  source  of  heat  is  to  be  sought  for  in  the  chemic  decompositions  and 
hydrations  taking  place  during  the  general  process  of  nutrition,  and  in  the 
combustion  of  the  carbonaceous  compounds  by  the  oxygen  of,  the  inspired 
air  ;  the  amount  of  its  production  is  in  proportion  to  the  activity  of  the  in- 
ternal changes. 

Every  contraction  of  a  muscle,  every  act  of  secretion,  each  exhibition  of 
nerve  force,  is  accompanied  by  a  change  in  the  chemic  composition  of  the 
tissues  and  an  evolution  of  heat.  The  reduction  of  the  disintegrated 
tissues  to  their  simplest  form  by  oxidation,  and  the  combination  of  the  oxy- 
gen of  the  inspired  air  with  the  carbon  and  hydrogen  of  the  blood  and  tis- 
sues, results  in  the  formation  of  carbonic  acid  and  water  and  the  generation 
of  a  great  amount  of  heat. 

Certain  elements  of  the  food,  particularly  the  non-nitrogenized  sub- 
stances, undergo  oxidation  without  taking  part  in  the  formation  of  the  tis- 
sues, being  transformed  into  carbonic  acid  and  water,  and  thus  increase 
the  sum  of  heat  in  the  body. 

Heat-producing  Tissues. — All  the  tissues  of  the  body  add  to  the 
general  amount  of  heat,  according  to  the  degree  of  their  activity.  But 
special  structures,  on  account  of  their  mass  and  the  large  amount  of 
blood  they  receive,  are  particularly  to  be  regarded  as  heat  producers,  e.  g.: 

1.  During  mental  activity  the  brain  receives  nearly  one  fifth  of  the  entire 
volume  of  blood,  and  the  venous  blood  returning  from  it  is  charged  with 
waste  matters,  and  its  temperature  is  increased. 

2.  The  muscular  tissue,  on  account  of  the  many  chemic  changes  occurring 
during  active  contractions,  must  be  regarded  as  the  chief  heat-producing 
tissue. 

3.  The  secreting  glands,  during  their  functional  activity,  add  largely  to  the 
amount  of  heat. 

The  entire  quantity  of  heat  generated  within  the  body  has  been  demon- 
strated experimentally  to  be  about  2,300  calories,  a  calory,  or  heat  unit, 
being  that  amount  of  heat  required  to  raise  the  temperature  of  one  kilogram 
of  water  (2.2  pounds)  1°  C.      This  quantity  of  heat,  if  not  utilized  and  re- 


SECRETION.  145 

tained  within  ths  body,  would  elevate  its  temperature  in  twenty-four  hours 
about  6o°  F.  That  this  volume  of  heat  depends  very  largely  upon  the 
oxidation  of  the  food -stuffs  can  be  shown  experimentally. 

The  normal  temperature  of  the  body  is  maintained  by  a  constant  expen- 
diture of  the  heat  in  several  directions  : 

1.  In  warming  the  food,  drink,  and  air  that  are  consumed  in  twenty-four 
hours.     For  this  purpose  about  157  heat  units  are  required. 

2.  In  evaporating  water  from  the  skin  and  lungs,  619  heat  units  being 
utilized  for  this  purpose. 

3.  In  radiation  and  conduction.  By  these  processes  the  body  loses  at 
least  fifty  per  cent,  of  its  heat,  or  1,156  heat  units. 

4.  In  the  production  of  work  ;  the  work  of  the  circulatory,  respiratory, 
muscidar,  and  nervous  apparatus  being  performed  by  the  transformation 
of  369  heat  units  into  units  of  work. 

The  nervous  system  influences  the  production  of  heat  in  a  part  by  increas- 
ing the  amount  of  blood  passing  through  it  by  its  action  upon  the  vasomotor 
nerves.  Whether  there  exists  a  special  heat-center  has  not  been  satisfac- 
torily determined,  though  this  is  probable. 


SECRETION. 

The  process  of  secretion  consists  in  the  separation  of  materials  from 
the  blood  which  are  either  to  be  again  utilized  to  fulfil  some  special  pur- 
pose in  the  economy,  or  are  to  be  removed  from  the  body  as  excrementi- 
tious  matter  ;  in  the  former  case  they  constitute  the  secretions,  in  the  latter, 
the  excretions. 

The  materials  which  enter  into  the  composition  of  the  secretions  are 
derived  from  the  nutritive  principles  of  the  blood,  and  require  special 
organs — e.  g.,  gastric  glands,  mammary  glands,  etc. — for  their  proper 
elaboration. 

The  materials  which  compose  the  excretions  preexist  in  the  blood,  and 
are  the  results  of  the  activities  of  the  nutritive  process  ;  if  retained  within 
the  body,  they  exert  a  deleterious  influence  upon  the  composition  of  the 
blood. 

Destruction  of  a  secreting  gland  abolishes  the  secretion  peculiar  to  it, 
and  it  can  not  be  formed  by  any  other  gland  ;  but  among  the  excreting 
organs  there  exists  a  complementary  relation,  so  that  if  the  function  of  one 
organ  be  interfered  with,  another  performs  it  to  a  certain  extent. 


146  HUMAN   PHYSIOLOGY. 

CLASSIFICATION  OF  THE  SECRETIONS. 

PERMANENT   FLUIDS. 

Serous  fluids.  Vitreous  humor  of  the  eye. 

Synovial  fluid.  Fluid  of  the  labyrinth  of  the  internal 

Aqueous  humor  of  the  eye.  ear. 

Cerebro-spinal  fluid. 

TRANSITORY    FLUIDS. 

Mucus.  Gastric  juice. 

Sebaceous  matter.  Pancreatic  juice. 

Cerumen  (external  meatus).  Secretion  from  B  runner's  glands. 

Meibomian  fluid.  Secretion  from  Lieberkiihn's  glands. 

Milk  and  colostrum.  Secretions  from  follicles  of  the  large 

Tears.  intestine. 

Saliva.  Bile  (also  an  excretion). 

EXCRETIONS. 

Perspiration  and  the  secretion  of         Urine. 

the  axillary  glands.  Bile  (also  a  secretion). 

FLUIDS    CONTAINING   FORMED   ANATOMIC   ELEMENTS. 

Seminal  fluid,  containing  sperma-         Fluid  of  the  Graafian  follicles, 
tozoids. 

The  essential  apparatus  for  secretion  is  a  delicate,  homogeneous, 
structureless  membrane,  on  one  side  of  which,  in  close  contact,  is  a  capil- 
lary plexus  of  blood-vessels,  and  on  the  other  side  a  layer  of  cells  the 
physiologic  function  of  which  varies  in  different  situations. 

Secreting  organs  may  be  divided  into  membranes  and  glands. 

Serous  membranes  usually  exist  as  closed  sacs,  the  inner  surfaces  of  which 
are  covered  by  pale,  nucleated  epithelium,  containing  a  small  amount  of 
secretion. 

The  serous  membranes  are  the  pleura,  peritoneum,  pei'icardium,  synovial 
sacs,  etc. 

The  serous  fluids  are  of  a  pale  amber  color,  somewhat  viscid,  alkaline, 
coagulable  by  heat,  and  resemble  the  serum  of  the  blood  ;  their  amount 
is  but  small.  The  pleural  fluid  varies  from  four  to  seven  drams  ;  the  peri- 
toneal from  one  to  four  ounces  ;  the  pericardial  from  one  to  three  drams. 

The  synovial  fluid 'is  colorless,  alkaline,  and  extremely  viscid,  from  the 
presence  of  synovin. 


SECRETION.  147 

The  function  of  serous  fluids  is  to  moisten  the  opposing  surfaces,  so  as 
to  prevent  friction  during  the  play  of  the  viscera. 

The  mucous  membranes  are  soft  and  velvety  in  character,  and  line  the 
cavities  and  passages  leading  to  the  exterior  of  the  body — e.  g.,  the  gastro- 
intestinal, pulmonary  and  genito-urinary.  They  consist  of  a  primary 
basement  membrane  covered  with  epithelial  cells,  which  in  some  situations 
are  tessellated,  in  others,  columnar. 

Mucus  is  a  pale,  semitransparent,  alkaline  fluid,  containing  epithelial 
cells  and  leukocytes.  It  is  composed,  chemically,  of  water,  an  albuminous 
principle  (mucosin),  and  mineral  salts  ;  the  principal  varieties  are  nasal, 
bronchial,  vaginal,  and  urinary. 

Secreting  glands  are  formed  of  the  same  elements  as  the  secreting 
membranes,  but  instead  of  presenting  flat  surfaces,  are  involuted,  forming 
tubules,  which  may  be  simple  follicles — e.  g.,  mucous,  uterine,  or  intestinal  ; 
or  compound follicles — e.g.,  gastric  glands,  mammary  glands,  or  racemose 
glands — e.  g.,  salivary  glands  and  pancreas.  They  are  composed  of  a 
basement  membrane,  enveloped  by  a  plexus  of  blood-vessels,  and  are  lined 
by  epithelial  and  true  secreting  cells,  which  in  different  glands  possess  the 
capability  of  elaborating  elements  characteristic  of  their  secretions. 

In  the  production  of  the  secretion  two  essentially  different  processes 
are  concerned. 

1.  Chemic. — The  formation  and  elaboration  of  the  characteristic  organic 
ingredients  of  the  secreted  fluids — e.  g.,  pepsin,  pancreatin — take  place 
during  the  intervals  of  glandular  activity,  as  a  part  of  the  general  func- 
tion of  nutrition.  They  are  formed  by  the  cells  lining  the  glands,  and 
can  often  be  seen  in  their  interior  with  the  aid  of  the  microscope — e.  g., 
bile  in  the  liver  cells,  fat  in  the  cells  of  the  mammary  gland. 

2.  Physical. — Consisting  of  a  transudation  of  water  and  mineral  salts  from 
the  blood  into  the  interior  of  the  gland. 

During  the  intervals  of  glandular  activity  only  that  amount  of  blood 
passes  through  the  gland  sufficient  for  proper  nutrition  ;  when  the  gland 
begins  to  secrete,  under  the  influence  of  an  appropriate  stimulus,  the  blood- 
vessels dilate  and  the  quantity  of  blood  becomes  greatly  increased  beyond 
that  flowing  to  the  gland  during  its  repose. 

Under  these  conditions  a  transudation  of  water  and  salt  takes  place, 
washing  out  the  characteristic  ingredients,  which  are  discharged  by  the 
gland  ducts.  The  discharge  of  the  secretions  is  intermittent ;  they  are 
retained  in  the  glands  until  they  receive  the  appropriate  stimulus,  when 


148  HUMAN   PHYSIOLOGY. 

they  pass  into  the  larger  ducts  by  the  vis  a  tergo,  and  are  then  discharged 
by  the  contraction  of  the  muscular  walls  of  the  ducts. 

The  activity  of  grandular  secretion  is  hastened  by  an  increase  in  the 
blood-pressure  and  retarded  by  a  diminution. 

The  nei~vous  centers  in  the  medulla  oblongata  influence  secretion  : 

1.  By  increasing  or  diminishing  the  amount  of  blood  entering  a  gland. 

2.  By  exerting  a  direct  influence  upon  the  secreting  cells  themselves,  the 
centers  being  excited  by  reflex  irritation,  mental  emotion,  etc. 


MAMMARY  GLANDS. 

The  mammary  glands,  which  secrete  the  milk,  are  two  more  or  less 
hemispheric  organs,  situated  in  the  human  female  on  the  anterior  surface 
of  the  chest.  Though  rudimentary  in  childhood,  they  gradually  increase 
in  size  as  the  young  female  approaches  puberty. 

The  gland  presents  at  its  convexity  a  small  prominence  of  skin  (the  nip- 
ple), which  is  surrounded  by  a  circular  area  of  pigmented  skin  (the  areola). 
The  gland  proper  is  covered  by  a  layer  of  adipose  tissue  anteriorly  and  is 
attached  posteriorly  to  the  pectoral  muscles  by  a  meshwork  of  fibrous  tissue. 
During  utero- gestation  the  mammary  glands  become  larger,  firmer,  and 
more  lobulated  ;  the  areola  darkens  and  the  veins  become  more  prominent. 
At  the  period  of  lactation  the  gland  is  the  seat  of  active  histologic  and 
physiologic  changes,  correlated  with  the  production  of  milk.  At  the  close 
of  lactation  the  glands  diminish  in  size,  undergo  involution,  and  gradually 
return  to  their  original  non-secreting  condition. 

Structure  of  the  Mammary  Glands. — Each  mammary  gland  consists 
of  an  aggregation  of  some  fifteen  or  twenty  lobes,  each  of  which  is  sur- 
rounded by  a  framework  of  fibrous  tissue.  The  lobe  is  provided  with  an 
excretory  duct,  which,  as  it  approaches  the  base  of  the  nipple,  expands 
to  form  a  sinus  or  reservoir,  beyond  which  it  opens  by  a  narrowed  orifice 
on  the  surface  of  the  nipple.  On  tracing  the  duct  into  a  lobe,  it  is  found  to 
divide  and  subdivide,  and  finally  to  terminate  in  lobules  or  acini.  Each 
acinus  consists  of  a  basement  membrane,  lined  by  low  polyhedral  cells. 
Externally  it  is  surrounded  by  connective  tissue,  supporting  blood-vessels, 
lymphatics,  and  nerves. 

MILK. 
Milk  is  an  opaque,  bluish-white  fluid,  almost  inodorous,  of  a  sweet  taste, 
an  alkaline  reaction,  and  a  specific  gravity  of  1025  to  1040.     When  exam- 


MAMMARY   GLANDS. 


149 


ined  microscopically  it  is  seen  to  consist  of  a  clear  fluid  (the  milk-plasma), 
holding  in  suspension  an  enormous  number  of  small,  highly  refractive  oil- 
globules,  which  measure,  on  an  average,  y<ny^  °^  an  lnc^  m  diameter, 
Each  globule  is  supposed  by  some  observers  to  be  surrounded  by  a  thin, 
albuminous  envelope,  which  enables  it  to  maintain  the  discrete  form.  The 
quantity  of  milk  secreted  daily  by  the  human  female  averages  about  two 
and  a  half  pints.  The  milk  of  all  the  mammalia  consists  of  all  the  differ- 
ent classes  of  nutritive  principles,  though  in  varying  proportions.  The 
relative  proportions  in  which  these  constituents  exist  are  shown  in  the  fol- 
lowing table  of  analyses  : 

COMPOSITION    OF   MILK. 


In  ioo  Parts. 

Human. 

Cow. 

Goat. 

Ass. 

Sheep. 

Mare. 

Water. 

88.OO 

86.87 

87-54 

91-57 

82.27 

88.80 

Caseinogen. 

2.40 

3-98 

3.00 

1.09 

6.IO 

2.I9 

Lactalbumin. 

0.57 

O.77 

O.62 

0.70 

I. OO 

O.42 

Fat. 

2.90 

3-50 

4.20 

1.02 

5-30 

2.50 

Lactose. 

5.87 

4.00 

4.00 

5-5o 

4.20 

5-5° 

Salts. 

O.16 

O.17 

O.56 

0.42 

1.00 

O.50 

Caseinogen  is  the  chief  proteid  constituent  of  milk,  and  is  held  in  so- 
lution by  the  presence  of  calcic  phosphate.  On  the  addition  of  acetic  acid 
or  of  sodic  chlorid  up  to  the  point  of  saturation,  the  caseinogen  is  precipi- 
tated as  such,  and  may  be  collected  by  appropriate  chemic  methods.  When 
taken  into  the  stomach  caseinogen  is  coagulated — that  is,  it  is  separated  into 
casein  or  tyrein  and  a  small  quantity  of  a  new  soluble  proteid.  The  fer- 
ment which  induces  this  change  is  known  as  rennin.  The  presence  of 
calcic  phosphate  is  necessary  for  this  coagulation. 

The  fat  of  milk  is  more  or  less  solid  at  ordinary  temperatures.  It  is  a 
composition  of  olein,  palmitin,  and  stearin,  with  a  small  quantity  of  butyrin 
and  caproin.  When  milk  is  allowed  to  stand  for  some  time  the  fat-glob- 
ules rise  to  the  surface  and  form  a  thick  layer,  known  as  cream.     When 


150  HUMAN   PHYSIOLOGY. 

subjected  to  the  churning  process,  the  fat  globules  run  together  and  form  a 
cohesive  mass — the  butter. 

Lactose  is  the  particular  form  of  sugar  characteristic  of  milk.  It  be- 
longs to  the  saccharose  group  and  has  the  following  composition  :  C12H22- 
On.  In  the  presence  of  the  bacillus  acidi  lactici  the  lactose  is  decomposed 
into  lactic  acid  and  carbon  dioxid,  the  former  of  which  will  cause  a  coagu- 
lation of  the  caseinogen. 

Mechanism  of  Secretion. — During  the  time  of  lactation  the  mam- 
mary gland  exhibits  periods  of  secretory  activity  which  alternate  with  pe- 
riods of  rest.  Coincidentally  with  these  periods,  certain  histologic  changes 
take  place  in  the  secreting  structures  of  the  gland.  At  the  close  of  a  period 
of  active  secretion  each  acinus  presents  the  following  features  :  the  epi- 
thelial cells  are  short,  cubic,  nucleated,  and  border  a  relatively  wide 
lumen  in  which  is  to  be  found  a  variable  quantity  of  non-discharged  milk. 
After  the  gland  has  rested  for  some  time,  active  metabolism  again  begins. 
The  epithelial  cells  grow  and  elongate  ;  the  nucleus  divides  into  two  or 
three  new  nuclei,  and  at  the  same  time  the  cell  becomes  constricted  ;  the 
inner  portion  is  detached  and  is  discharged  into  the  lumen.  Coincidentally 
with  these  changes  oil-globules  make  their  appearance  in  the  cell  proto- 
plasm, some  of  which  are  discharged  separately  into  the  lumen,  while  others 
remain  for  a  time  associated  with  the  detached  cell.  From  these  histo- 
logic changes  it  would  appear  that  the  caseinogen  and  the  fat-globules  are 
metabolic  products  of  the  cell  protoplasm,  and  not  derived  directly  from  the 
blood.  That  lactose  has  a  similar  origin  appears  certain  from  the  fact  that 
it  is  formed  independently  of  carbohydrate  food.  The  water  and  inorganic 
salts  are  doubtless  secreted  by  a  mechanism  similar  to  that  of  all  other 
secreting  glands. 


VASCULAR  OR  DUCTLESS  GLANDS. 

INTERNAL  SECRETIONS. 

The  metabolism  of  the  body  generally,  as  well  as  that  of  individual 
organs,  has  been  shown  to  be  related  not  only  to  the  physiologic  activity 
of  such  organs  as  the  liver  and  pancreas,  but  also  to  the  activity  of  the 
so-called  vascular  or  ductless  glands.  The  influence  of  the  pancreas 
in  regulating  the  production  of  glycogen  by  the  liver,  and  the  influence 
of  the  liver  in  the  maintenance  of  the  general  metabolism  through  the  pro- 


VASCULAR    OR    DUCTLESS   GLANDS.  151 

duction  of  glycogen  and  the  formation  of  urea,  are  now  established 
facts.  That  the  vascular  or  ductless  glands  to  an  equal  extent,  though 
perhaps  in  a  different  way,  assist  in  the  maintenance  of  physiologic  pro- 
cesses, appears  certain  from  the  results  of  animal  experimentation.  The 
explanation  given,  and  generally  accepted  at  the  present  time,  for  the  influ- 
ence of  these  glands  is  that  they  produce  specific  substances,  which  are 
poured  into  the  blood  or  lymph  and  carried  direct  to  the  tissues,  to  the 
activities  of  which  they  appear  to  be  essential ;  for  without  these  substances 
the  nutrition  of  the  tissues  declines  and  in  a  short  time  a  fatal  termination 
ensues. 

Inasmuch  as  these  partly  unknown  substances  are  formed  by  cell  activity 
and  are  poured  into  the  interstices  of  the  tissues,  they  have  been  termed 
"internal  secretions."  Though  the  term  internal  secretions  is  applicable 
to  all  substances  which  arise  in  consequence  of  tissue  metabolism,  and 
which,  after  being  poured  into  the  blood,  influence  in  varying  degrees  and 
ways  physiological  processes,  yet  the  term  in  this  connection  will  be  applied 
only  to  the  secretions  of  the  thyroid  gland,  hypophysis  cerebri,  and  adrenal 
bodies. 

Thyroid  Gland. — The  thyroid  gland  or  body  consists  of  two  lobes 
situated  on  the  lateral  aspect  of  the  upper  part  of  the  trachea.  Each  lobe 
is  pyriform  in  shape,  the  base  being  directed  downward  and  on  a  level 
with  the  fifth  or  sixth  tracheal  ring.  The  lobe  is  about  50  mm.  in  length, 
20  mm.  in  breadth,  and  25  mm.  in  thickness.  As  a  rule,  the  lobes  are 
united  by  a  narrow  band  or  isthmus  of  the  same  tissue.  In  color  the 
gland  is  reddish,  and  it  is  abundantly  supplied  with  blood-vessels  and 
lymphatics. 

Microscopic  examination  shows  that  the  thyroid  consists  of  an  enormous 
number  of  closed  sacs  or  vesicles,  variable  in  size,  the  largest  not  meas 
uring  more  than  o.  I  mm.  in  diameter.  Each  sac  is  composed  of  a  thin 
homogeneous  membrane  lined  by  cuboid  epithelium.  The  interior  of  the 
sac  in  adult  life  contains  a  transparent  viscid  fluid,  containing  albumin  and 
termed  "  colloid  "  substance.  Externally,  the  sacs  are  surrounded  by  a 
plexus  of  capillary  blood-vessels  and  lymphatics.  The  individual  sacs  are 
united  and  supported  by  connective  tissue,  which  forms,  in  addition,  a 
covering  for  the  entire  gland. 

Function  of  the  Thyroid. — The  knowledge  at  present  possessed  as  to 
the  function  of  the  thyroid  gland,  especially  in  mammals,  is  the  outcome  of 
a  study  of  the  effects  which  follow  its  arrest  of  development  in  the  child, 
its  degeneration  in  the  adult,  its  extirpation  in  the  human  being  as  well  as 


152  HUMAN   PHYSIOLOGY. 

in  animals.  The  results,  however,  which  follow  its  extirpation  are  not 
always  uniform  in  all  animals  ;  sufficient  reasons  for  which  lack  of  uni- 
formity can  not  always  be  assigned. 

Cretinism,  a  condition  characterized  by  a  want  of  physical  and  mental 
development,  is  associated  with,  if  not  directly  dependent  on,  a  congenital 
absence  or  an  arrested  development  of  the  thyroid,  either  at  the  time  of 
birth  or  during  the  early  years  of  childhood. 

Myxedema,  a  condition  of  the  skin  in  which  there  is  a  hyperplasia  of  the 
connective  tissue,  of  an  embryonic  type,  rich  in  mucin,  is  generally  re- 
garded as  one  of  the  effects  of  degenerative  processes  in  the  thyroid. 
Partly  in  consequence  of  this  change  in  the  skin  the  face  becomes  broader, 
swollen,  and  flattened,  giving  rise  to  a  loss  of  expression.  At  the  same 
time  the  mind  becomes  dull,  clouded,  even  approximating  the  idiotic  type. 
This  supposed  infiltration  of  the  skin  with  mucin  was  termed  myxedema  by 
Ord,  who  at  the  same  time  associated  it  with  a  change  in  the  structure  of 
the  thyroid  as  a  result  of  which  it  became  functionally  useless. 

Extirpation  of  the  thyroid,  for  relief  from  symptoms  due  to  grave  patho- 
logic changes,  has  been  followed  in  human  beings  by  symptoms  similar  to 
those  of  myxedema.  To  this  condition  the  terms  operative  myxedema  and 
cachexia  strumipriva  have  been  applied. 

After  the  publication  of  the  history  of  the  myxedema  which  followed 
surgical  removal  of  the  thyroid,  Schiff,  in  1 887,  repeated  his  earlier  experi- 
ments on  dogs,  and  found  again  that  removal  of  the  thyroid  was  speedily  fol- 
lowed by  tremors,  convulsions,  and  death.  Similar  experiments  were  made 
by  Horsley  on  monkeys,  with  results  which  resembled  those  characteristic 
of  myxedema.  Among  the  symptoms  which  developed  within  a  few  days 
after  the  removal  of  the  gland  may  be  mentioned  loss  of  appetite  ;  fibrillar 
contractions  of  muscles  ;  tremors  ;  spasms  ;  mucinoid  degeneration  of  the 
skin,  giving  rise  to  puffiness  of  the  eyelids  and  face  and  to  a  swollen  con- 
dition of  the  abdomen  ;  hebetude  of  mind,  frequently  terminating  in  idiocy  ; 
fall  of  blood-pressure ;  dyspnea ;  albuminuria ;  atrophy  of  the  tissues, 
followed  by  death  of  the  animal  in  the  course  of  from  five  to  eight  weeks. 
The  complexus  of  symptoms  observed  in  monkeys  was  divided  by  Horsley 
into  three  stages:  vix.,  the  neurotic,  the  mucinoid,  and  the  atrophic.  It 
is  evident  that  the  presence  of  the  thyroid  is  essential  to  the  normal  activity 
of  the  tissues  generally.  As  to  the  manner  in  which  it  exerts  its  favorable 
influence,  there  is  some  difference  of  opinion.  The  view  that  the  gland 
removes  from  the  blood  certain  toxic  bodies,  rendering  them  innocuous,  and 
thus  preserving  the  body  from  a  species  of  auto-intoxication,  is  gvadually 
yielding  to  the  more  probable  view  that  the  epithelium  is  engaged  to  the 


VASCULAR    OR    DUCTLESS   GLANDS.  153 

secretion  of  a  specific  material,  which  finds  its  way  into  the  blood  or 
lymph  and  in  some  unknown  way  influences  favorably  tissue  metabolism. 
This  view  of  the  function  of  the  thyroid  is  supported  by  the  fact  that  suc- 
cessful grafting  of  a  portion  of  the  thyroid  beneath  the  skin  or  in  the 
abdominal  cavity  will  prevent  the  usual  symptoms  which  follow  thyroidec- 
tomy. The  same  result  is  obtained  by  the  intravenous  injection  of  thyroid 
juice  or  by  the  administration  of  the  raw  gland.  It  was  shown  by  Murray 
that  myxedematous  patients  could  be  benefited,  and  even  cured,  by  feed- 
ing them  with  fresh  thyroids  or  even  with  the  dry  extract. 

The  chemic  features  of  the  material  secreted  and  obtained  from  the 
structures  of  the  thyroid  indicate  that  it  is  a  complex  proteid  containing 
iodin,  which,  under  the  influence  of  various  reagents,  undergoes  cleavage, 
giving  rise  to  a  non-proteid  residue,  which  carries  with  it  the  iodin  and 
phosphorus.  The  amount  of  iodin  in  the  thyroid  varies  from  0.33  to  I 
milligram  for  each  gram  of  tissue.  To  this  compound  the  term  thyro- 
iodin  has  been  given.  The  administration  of  this  compound  produces 
effects  similar  to  those  which  follow  the  therapeutic  administration  of  the 
fresh  thyroid  itself:  viz.,  a  diminution  of  all  myxedematous  symptoms. 
In  normal  states  of  the  body,  thyroiodin  influences  very  actively  the  gen- 
eral metabolism.  It  gives  rise  to  a  decomposition  of  fats  and  proteids  and 
to  a  decline  in  body-weight.  In  large  doses  it  may  produce  toxic  symp- 
toms :  e.  g,,  increased  cardiac  action,  vertigo,  and  glycosuria. 

The  Hypophysis  Cerebri. — This  is  a  small  body  lodged  in  the  sella 
turcica  of  the  sphenoid  bone.  It  consists  of  an  anterior  lobe,  somewhat 
red  in  color,  and  a  posterior  lobe,  yellowish-gray  in  color.  The  former  is 
much  the  larger  and  partly  embraces  the  latter.  The  anterior  lobe  is 
developed  from  an  invagination  of  the  epiblast  of  the  mouth  cavity,  and 
consists  of  distinct  gland  tissue.  The  posterior  lobe  is  an  outgrowth  from 
the  brain,  and  is  connected  with  the  infundibulum  by  a  short  stalk.  It  has 
been  suggested  that  the  term  infundibular  body  be  reserved  for  the  posterior 
lobe.  This  distinction  appears  to  be  desirable,  inasmuch  as  in  their  origin 
and  structure  they  are  separate  and  distinct  bodies. 

Removal  of  the  hypophysis  cerebri,  or  the  pituitary  body,  is  always 
followed  by  a  fatal  result,  preceded  by  symptoms  not  unlike  those  which 
follow  removal  of  the  thyroid  :  viz.,  anorexia,  tremors,  spasms,  etc. 
Degeneration  of  the  hypophysis  has  been  found  in  connection  with  a  hy- 
pertrophic condition  of  the  bones  of  the  face  and  extremities,  to  which  the 
term  acromegalia  has  been  given. 

Intravenous  injection  of  an  extract  of  the  hypophysis  increases  the 
II 


154  HUMAN    PHYSIOLOGY. 

force  of  the  heart-beat  without  any  change  in  its  frequency,  and  causes  a 
rise  of  blood-pressure  from  a  stimulation  of  the  arterioles  (Schafer  and 
Oliver).  The  material  secreted  by  the  hypophysis  has  not  been  isolated, 
hence  its  chemic  features  are  unknown.  After  its  formation  it  probably 
passes  through  a  system  of  ducts  into  the  cerebrospinal  fluid,  after  which 
it  influences  the  metabolism  of  the  nervous  and  osseous  tissues  as  well  as 
the  force  of  the  heart  muscle. 

An  extract  of  the  hypophysis  itself  exerts  no  appreciable  effect  on  the 
blood-pressure  or  on  the  rate  of  the  heart-beat,  nor  does  it  influence  the 
circulatory  and  respiratory  organs  (Howell).  An  extract  of  the  infundib- 
ular body  intravenously  injected,  however,  gives  rise  to  increased  blood- 
pressure  and  to  a  slowing  of  the  heart-beat. 

Adrenal  Bodies,  or  Suprarenal  Capsules. — These  are  two  flattened 
bodies,  somewhat  crescentic  or  triangular  in  shape,  situated  each  upon  the 
upper  extremity  of  the  corresponding  kidney,  and  held  in  place  by  con- 
nective tissue.  They  measure  about  40  mm.  in  height,  30  mm.  in  breadth, 
and  from  6  to  8  mm.  in  thickness.     The  weight  of  each  is  about  4  gm. 

Function  of  the  Adrenal  Bodies. — It  was  observed  by  Addison  that 
a  profound  disturbance  of  the  nutrition,  characterized  by  a  bronze-like 
discoloration  of  the  skin  and  mucous  membranes  of  the  mouth,  extreme 
muscular  weakness,  and  profound  anemia,  was  associated  with,  if  not 
dependent  on,  pathologic  conditions  of  the  suprarenal  glands.  In  the  prog- 
ress of  the  disease  the  asthenia  gradually  increases,  the  heart  becomes 
weak,  the  pulse  small,  soft,  and  feeble,  indicating  a  general  loss  of  tone  of 
the  muscular  and  vascular  apparatus.  Death  ensues  from  paralysis  of  the 
respiratory  muscles.  The  essential  nature  of  the  lesion  which  gives  rise  to 
these  symptoms  has  not  been  determined. 

Removal  of  these  bodies  from  various  animals  is  invariably  and  in  a 
short  time  followed  by  death,  preceded  by  some  of  the  symptoms  charac- 
teristic of  Addison's  disease.  Their  development,  however,  was  more 
acute.  From  the  fact  that  animals  so  promptly  die  from  extirpation  of 
these  bodies,  and  the  further  fact  that  the  blood  of  such  animals  is  toxic  to 
those  the  subjects  of  recent  extirpation,  but  not  to  normal  animals,  the 
conclusion  was  drawn  that  the  function  of  the  adrenal  bodies  was  to 
remove  from  the  blood  some  toxic  material  the  product  of  muscle  metab- 
olism. Its  accumulation  after  extirpation  gives  rise  to  death  through 
auto-intoxication. 

On  the  supposition  that  the  adrenals  might  secrete  and  pour  into  the 
blood  a  specific  material  which  favorably  influences  general  ^metabolism, 


KIDNEYS.  155 

Schafer  and  Oliver  injected  hypodermically  glycerin  and  water  extracts, 
and  observed  at  once  an  increased  activity  of  the  heart-beats  and  of  the 
respiratory  movements.  The  effects,  however,  were  only  transitory.  When 
these  extracts  are  injected  into  the  veins  directly,  there  follows  in  a 
short  time  a  cessation  of  the  auricular  contraction  of  the  heart,  though  the 
ventricular  contraction  continues  with  an  independent  rhythm.  If  the  vagi 
are  cut  previous  to  the  injection  or  if  the  inhibition  is  removed  by  atropin, 
the  rapidity  and  vigor  of  both  auricles  and  ventricles  are  increased.  Whether 
the  inhibitory  influence  is  removed  or  not,  there  is  a  marked  increase  in  the 
blood- pressure,  though  it  is  greater  in  the  former  than  in  the  latter  instance. 
This  is  attributed  to  a  direct  stimulation  and  contraction  of  the  muscle- 
fibers  of  the  arterioles  themselves,  and  not  to  vaso-motor  influences,  as  it 
occurs  also  after  division  of  the  cord  and  destruction  of  the  bulb.  The 
contraction  of  the  arterioles  is  quite  general,  as  shown  by  plethysmographic 
studies  of  the  limbs,  spleen,  kidney,  etc.  Applied  locally  to  the  mucous 
membranes,  the  adrenal  extract  produces  contraction  of  the  blood-vessels 
and  pallor.  The  skeletal  muscles  are  affected  by  the  extract  very  much  as 
they  are  by  veratrin.  The  duration  of  a  single  contraction  is  very  much 
prolonged,  especially  in  the  phase  of  relaxation  or  of  decreasing  energy. 

It  is  evident  from  these  experiments  that  the  adrenal  bodies  are  engaged 
in  elaborating  and  pouring  into  the  blood  a  specific  material  which  stimu- 
lates to  increased  activity  the  muscle-fibers  of  the  heart  and  arteries,  and 
thus  assists  in  maintaining  the  normal  blood-pressure  as  well  as  the  tonicity 
of  the  skeletal  muscles.  The  active  principle  of  this  gland  has  been  iso- 
lated by  Abel  and  termed  epinephrin. 

EXCRETION. 

The  principal  excrementitious  fluids  discharged  from  the  body  are 
the  urine,  perspiration,  and  bile  ;  they  hold  in  solution  principles  of  waste 
which  are  generated  during  the  activity  of  the  nutritive  process  and  are 
the  ultimate  forms  to  which  the  organic  constituents  are  reduced  in  the 
body.     They  also  contain  inorganic  salts. 

The  urinary  apparatus  consists  of  the  kidneys,  ureters,  and  bladder. 

KIDNEYS. 

The  kidneys  are  the  organs  for  the  secretion  of  urine  ;  they  resemble 
a  bean  in  shape,  are  from  four  to  five  inches  in  length,  two  in  breadth, 
and  weigh  from  four  to  six  ounces. 


156 


HUMAN    PHYSIOLOGY. 


They  are  situated  in  the  lumbar  region,  one  on  each  side  of  the  vertebral 
column  behind  the  peritoneum,  and  extend  from  the  eleventh  rib  to  the  crest 


Fig.    19. — Longitudinal  Section  through    the   Kidney,  the   Pelvis   of  the 
Kidney,  and  a  number  of  Renal  Calyces. — {Tyson,  after  Henle.) 

A.  Branch  of  the  renal  artery.  U.  Ureter.  C.  Renal  calyx.  1.  Cortex.  1'.  Medul- 
lary rays.  1".  Labyrinth,  or  cortex  proper.  2.  Medulla.  2'.  Papillary  portion  of 
medulla,  or  medulla  proper.  2".  Border  layer  of  the  medulla.  3,  3.  Transverse 
section  through  the  axes  of  the  tubules  of  the  border  layer.  4.  Fat  of  the  renal 
sinus.     5,  5.  Arterial  branches.     *.   Transversely  coursing  medulla  rays. 

of  the  ilium  ;  the  anterior  surface  is  convex,  the  posterior  surface  concave, 
the  latter  presenting  a  deep  notch,  the  hilus. 

The  kidney  is  surrounded  by  a  thin,  smooth  membrane  composed  of 


KIDNEYS. 


157 


white  fibrous  and  yellow  elastic  tissue  ;  though  it  is  attached  to  the  surface 
of  the  kidney  by  minute  processes  of  connective  tissue,  it  can  be  readily 
torn  away.     The  substance  of  the  kidney  is  dense,  but  friable. 

Upon  making  a  longitudinal  section  of  the  kidney  it  will  be  observed 
that  the  hilus  extends  into  the  interior  of  the  organ  and  expands  to  form 
a  cavity  known  as  the  sinus.  This  cavity  is  occupied  by  the  upper,  dilated 
portion  of  the  ureter,  the  interior  of  which  forms  the  pelvis.  The  ureter 
subdivides  into  several  portions,  which  ultimately  give  origin  to  a  number 
of  smaller  tubes,  termed  calyces,  which  receive  the 
apices  of  the  pyramids. 

The  parenchyma  of  the  kidney  consists  of 
two  portions — viz.  : 

1.  An  internal  or  medullary  portion,  consisting 
of  a  series  of  pyramids  or  cones,  some  twelve 
or  fifteen  in  number.  They  present  a  dis- 
tinctly striated  appearance,  a  condition  due 
to  the  straight  direction  of  the  tubules  and 
blood-vessels. 

2.  An  external  or  cortical  portion,  consisting  of  a 
delicate  matrix  containing  an  immense  number 
of  tubules  having  a  markedly  convoluted  ap- 
pearance. Throughout  its  structure  are  found 
numerous  small  ovoid  bodies,  termed  Mal- 
pighian  corpuscles. 

The  Uriniferous  Tubules. — The  kidney  is  a 
compound,  tubular  gland  composed  of  micro- 
scopic tubules  whose  function  it  is  to  secrete 
from  the  blood  those  waste  products  which  col- 
lectively constitute  the  urine.  If  the  apex  of 
each  pyramid  be  examined  with  a  lens,  it  will 
present  a  number  of  small  orifices,  which  are  the 
beginnings  of  the  uriniferous  tubules.  From 
this  point  the  tubules  pass  outward  in  a  straight 
but  somewhat  divergent  manner  toward  the  cortex,  giving  off  at  acute 
angles  a  number  of  branches  (Fig.  20).  From  the  apex  to  the  base  of  the 
pyramids  they  are  known  as  the  tubules  of  Bellini.  In  the  cortical  portion 
of  the  kidney  each  tubule  becomes  enlarged  and  twisted,  and  after  pur- 
suing an  extremely  convoluted  course,  turns  backward  into  the  medullary 
portion  for  some  distance,  forming  the  descending  limb  of  Henle's  loop  : 


Fig.  20. — Diagrammatic 
Exposition  of  the 
Method  in  which 
the  Uriniferous 
Tubes  Unite  to 
Form  Primitive 
Cones.  —  ( Tyson, 
after  Ludnvig.) 


158  HUMAN   PHYSIOLOGY. 

it  then  turns  upon  itself,  forming  the  ascending  limb  of  the  loop,  reenters 
the  cortex,  again  expands,  and  finally  terminates  in  a  spheric  enlargement 
known  as  Midler'' s  or  Boivmari 's  capsule.  Within  this  capsule  is  contained 
a  small  tuft  of  blood-vessels,  constituting  the  glomerulus,  or  Malpighian 
corpuscle. 

Structure  of  the  Tubules. — Each  tubule  consists  of  a  basement  mem- 
brane lined  by  epithelial  cells  throughout  its  entire  extent.  The  tubule 
and  its  contained  epithelium  vary  in  shape  and  size  in  different  parts  of 
its  course.  The  termination  of  the  convoluted  tube  consists  of  a  little  sac 
or  capsule,  which  is  ovoid  in  shape  and  measures  about  ^i^  of  an  inch. 
This  capsule  is  lined  by  a  layer  of  flattened  epithelial  cells,  which  is 
also  reflected  over  the  surface  of  the  glomerulus.  During  the  periods  of 
secretory  activity  the  blood-vessels  of  the  glomerulus  become  filled  with 
blood,  so  that  the  cavity  of  the  sac  is  almost  obliterated  ;  after  secretory 
activity  the  blood-vessels  contract  and  the  sac- cavity  becomes  enlarged. 
In  that  portion  of  the  tubule  lying  between  the  capsule  and  Henle's  loop 
the  epithelial  cells  are  cuboid  in  shape;  in  Henle's  loop  they  are  flat- 
tened, while  in  the  remainder  of  the  tubule  they  are  cuboid  and 
columnar. 

Blood-vessels  of  the  Kidney. — The  renal  artery  is  of  large  size  and 
enters  the  organ  at  the  hilum  ;  it  divides  into  several  large  branches,  which 
penetrate  the  substance  of  the  kidney  between  the  pyramids,  at  the  base 
of  which  they  form  an  anastomosing  plexus,  which  completely  surrounds 
them.  From  this  plexus  vessels  follow  the  straight  tubes  toward  the  apex, 
while  others,  entering  the  cortical  portion,  divide  into  small  twigs,  which 
enter  the  Malpighian  body  and  form  a  mass  of  convoluted  vessels,  the 
glomerulus.  After  circulating  through  the  Malpighian  tuft,  the  blood  is 
gathered  together  by  two  or  three  small  veins,  which  again  subdivide  and 
form  a  fine  capillary  plexus,  which  envelops  the  convoluted  tubules  ;  from 
this  plexus  the  veins  converge  to  form  the  emulgent  vein,  which  empties 
into  the  vena  cava. 

The  nerves  of  the  kidney  follow  the  course  of  the  blood-vessels  and 
are  derived  from  the  renal  plexus. 

The  ureter  is  a  membranous  tube,  situated  behind  the  peritoneum, 
about  the  diameter  of  a  goose-quill,  eighteen  inches  in  length,  and  extends 
from  the  pelvis  of  the  kidney  to  the  base  of  the  bladder,  which  it  perforates 
in  an  oblique  direction.  It  is  composed  of  three  coats  :  fibrous,  muscular, 
and  mucous. 

The  bladder  is  a  reservoir  for  the   temporary  reception  of  the  urine 


URINE.  159 

prior  to  its  expulsion  from  the  body;  when  fully  distended  it  is  ovoid  in 
shape,  and  holds  about  one  pint.  It  is  composed  of  four  coats  :  serous, 
muscular  (the  fibers  of  which  are  arranged  longitudinally  and  circularly), 
areolar,  and  mucous.  The  orifice  of  the  bladder  is  controlled  by  the 
sphincter  vesit a i  a  muscular  band  about  x/,  of  an  inch  in  width. 

As  soon  as  the  urine  is  formed  it  passes  through  the  tubuli  uriniferi 
into  the  pelvis  and  thence  through  the  ureters  into  the  bladder,  which  it 
enters  at  an  irregular  rate.  Shortly  after  a  meal,  after  the  ingestion  of 
large  quantities  of  fluid,  and  after  exercise,  the  urine  flows  into  the  bladder 
quite  rapidly,  while  it  is  reduced  to  a  few  drops  during  the  intervals  of 
digestion.  It  is  prevented  from  regurgitating  into  the  ureters  by  the 
oblique  direction  they  take  between  the  mucous  and  muscular  coats. 

Nervous  Mechanism  of  Urination. — "When  the  urine  has  passed  into 
the  bladder,  it  is  there  retained  by  the  sphincter  vesicas  muscle,  kept  in  a 
state  of  chronic  contraction  by  the  action  of  a  nerve  center  in  the  lumbar 
region  of  the  spinal  cord.  This  center  can  be  inhibited  and  the  sphincter 
relaxed,  either  reflexly,  by  impressions  coming  through  sensory  nerves  from 
the  mucous  membrane  of  the  bladder,  or  directly,  by  a  voluntary  impulse 
descending  the  spinal  cord.  When  the  desire  to  urinate  is  experienced, 
impressions  made  upon  the  vesical  sensory  nerves  are  carried  to  the  centers 
governing  the  sphincter  and  detrusor  urince  muscles  and  to  the  brain.  If 
now  the  act  of  urination  is  to  take  place,  a  voluntary  impulse  originating  in 
the  brain  passes  down  the  spinal  cord  and  still  further  inhibits  the  sphincter 
vesicae  center,  with  the  effect  of  relaxing  the  muscle  and  of  stimulating 
the  center  governing  the  detrusor  muscle,  with  the  effect  of  contracting  the 
muscle  and  expelling  the  urine.  If  the  act  is  to  be  suppressed,  voluntary 
impulses  inhibit  the  detrusor  center  and  possibly  stimulate  the  sphincter 
center. 

The  genitospinal  center  controlling  these  movements  is  situated  in  that 
portion  of  the  spinal  cord  corresponding  to  the  origin  of  the  third,  fourth, 
and  fifth  sacral  nerves. 

URINE. 

Normal  urine  is  of  a  pale  yellow  or  amber  color,  perfectly  transparent, 
with  an  aromatic"  odor,  an  acid  reaction,  a  specific  gravity  of  1020,  and  a 
temperature  when  first  discharged  of  loo°  F. 

The  color  varies  considerably  in  health,  from  a  pale  yellow  to  a  brown 
hue,  owing  to  the  presence  of  the  coloring-matter,  urobilin  or  urochrome. 


160 


HUMAN    PHYSIOLOGY. 


The  transparency  is  diminished  by  the  presence  of  mucus,  the  calcium 
and  magnesium  phosphates,  and  the  mixed  urates. 

The  reaction  of  the  urine  is  acid,  owing  to  the  presence  of  acid  phos- 
phate of  sodium.  The  degree  of  acidity,  however,  varies  at  different 
periods  of  the  day.  Urine  passed  in  the  morning  is  strongly  acid,  while 
that  passed  during  and  after  digestion,  especially  if  the  food  is  largely 
vegetable  in  character,  is  either  neutral  or  alkaline. 

The  specific  gravity  varies  from  1 015  to  1 025. 

The  quantity  of  urine  excreted  in  twenty-four  hours  is  between  forty  and 
fifty  fluidounces,  but  ranges  above  and  below  this  standard. 

The  odor  is  characteristic,  and  caused  by  the  presence  of  taurylic  and 
phenylic  acids,  but  is  influenced  by  vegetable  foods  and  other  substances 
eliminated  by  the  kidneys. 

COMPOSITION    OF   URINE. 

Water, 967.0 


Urea, 

Other  nitrogenized  crystalline  bodies,  uric  acid,  prin-' 

cipally  in  the  form  of  alkaline  urates, 
Creatin,  creatinin,  xanthin,  hypoxanthin, 
Hippuric  acid,  leucin,  tyrosin,  taurin,  cystin,  all  in 

small  amounts,  and  not  constant, 
Mucus  and  pigment, 


14.230 


10.635 


Salts 


Inorganic :  principally  sodium  and  potassium  sul- 
phates, phosphates,  and  chlorids,  with  magnesium 
and  calcium  phosphates,  traces  of  silicates  and 
chlorids, 

Organic :  lactates,  hippurates,  acetates,  formates, 
which  appear  only  occasionally, 

Sugar 

Gases  (nitrogen  and  carbonic  acid  principally). 


8.I3S 


a  trace 


1,000.000 


The  average  quantity  of  the  principal  constituents  excreted  in  twenty- 
four  hours  is  as  follows  : 

Water, 52.0  fluidounces. 

Urea,        512-4  grains. 

Uric  acid, ...       8.5        " 

Phosphoric  acid, 45-°       " 

Sulphuric  acid, 3I-H      " 

Inorganic  salts, 323. 25      " 

Lime  and  magnesia, 6.5        " 


URINE.  161 

To  determine  the  amount  of  solid  matters  in,  any  given  amount  of 
urine,  multiply  the  last  two  figures  of  the  specific  gravity  by  the  coefficient 
of  Haeser,  2.33 — e.  g.,  in  1,000  grains  of  urine  having  a  specific  gravity 
1022,  there  are  contained  22  X  2-33  =  51.26  grains  of  solid  matter. 

Organic  Constituents  of  Urine. — Urea  is  one  of  the  most  important 
of  the  organic  constituents  of  the  urine,  and  is  present  to  the  extent  of 
from  2.5  to  3.2  per  cent.  Urea  is  a  colorless,  neutral  substance,  crystalliz- 
ing in  four-sided  prisms  terminated  by  oblique  surfaces.  When  crystalliza- 
tion is  caused  to  take  place  rapidly,  the  crystals  take  the  form  of  long, 
silky  needles.  Urea  is  soluble  in  water  and  alcohol  ;  when  subjected  to 
prolonged  boiling,  it  is  decomposed,  giving  rise  to  carbonate  of  ammonia. 
In  the  alkaline  fermentation  of  urine,  urea  takes  up  two  molecules  of 
water  with  the  production  of  carbonate  of  ammonia. 

The  average  amount  of  urea  excreted  daily  has  been  estimated  at  about 
500  grains.  As  urea  is  one  of  the  principal  products  of  the  breaking  up  of 
the  albuminous  compounds  within  the  body,  it  is  quite  evident  that  the 
quantity  produced  and  eliminated  in  twenty-four  hours  will  be  increased  by 
any  increase  in  the  amount  of  albuminous  food  consumed,  or  by  a  rapid 
destruction  of  albuminous  tissues,  as  is  observed  in  various  pathologic 
states,  inanition,  febrile  conditions,  fevers,  etc.  A  farinaceous  or  vegetable 
diet  will  diminish  the  urea  production  nearly  one  half. 

Muscular  exercise  when  the  nutrition  of  the  body  is  in  a  state  of  equi- 
librium does  not  seem  to  increase  the  quantity  of  urea. 

Seat  of  Urea  Formation. — As  to  the  seat  of  urea  formation,  little 
is  positively  known.  It  is  quite  certain  that  it  preexists  in  the  blood  and  is 
merely  excreted  by  the  kidneys.  It  is  not  produced  in  muscles,  as  even 
after  prolonged  exercise  hardly  a  trace  of  urea  is  to  be  found  in  them. 
Experimental  and  pathologic  facts  point  to  the  liver  as  the  probable  organ 
engaged  in  urea  formation.  Acute  yellow  atrophy  of  the  liver,  suppura- 
tive diseases  of  the  liver,  diminish  almost  entirely  the  production  of  urea. 

Uric  acid  is  also  a  constant  ingredient  of  the  urine  and  is  closely  allied 
to  urea.  It  is  a  nitrogenized  substance,  carrying  out  of  the  body  a  large 
quantity  of  nitrogen.  The  amount  eliminated  daily  varies  from  five  to  ten 
grains.  Uric  acid  is  a  colorless  crystal  belonging  to  the  rhombic  system. 
It  is  insoluble  in  water,  and  if  eliminated  in  excessive  amounts,  it  is  de- 
posited as  a  "  brick -red"  sediment  in  the  urine.  It  is  doubtful  if  uric  acid 
exists  in  a  free  state,  being  combined  for  the  most  part  with  sodium  and 
potassium  bases  forming  urates.     It  is  to  be  regarded  as  one  of  the  termi- 


162  HUMAN    PHYSIOLOGY. 

nal  products  of  the  disassimilation  of  albuminous  compounds,  and  is  prob- 
ably produced  in  the  liver. 

Hippuric  acid  is  found  very  generally  in  urine,  though  it  is  present 
only  in  small  amounts.  It  is  increased  by  a  diet  of  asparagus,  cranberries, 
plums,  and  by  the  administration  of  benzoic  and  cinnamic  acids.  It  is 
probably  formed  in  the  kidney. 

Kreatinin  resembles  the  kreatin  derived  from  muscles.  It  is  a  color- 
less crystal,  belonging  to  the  rhombic  system.  Its  origin  is  unknown, 
though  it  is  largely  increased  in  amount  by  albuminous  food.  About 
fifteen  grains  are  excreted  daily. 

Xanthin,  sarkin,  oxaluric  acid,  and  allantoin  are  also  constituents 
of  urine.  They  are  nitrogenized  compounds  and  are  also  terminal  products 
of  albuminous  compounds. 

Urobilin,  the  coloring- matter  of  the  urine,  is  a  derivative  of  the  bile 
pigments.  It  is  particularly  abundant  in  febrile  conditions,  giving  to  the 
urine  its  reddish -yellow  color. 

Inorganic  Constituents  of  Urine. — Earthy  Phosphate.  Phos- 
phoric acid  in-  combination  with  magnesium  and  calcium  is  excreted  daily 
to  the  extent  of  from  fifteen  to  thirty  grains.  The  phosphates  are  insol- 
uble in  water,  but  are  held  in  solution  in  the  urine  by  its  acid  ingredients, 
alkalinity  of  the  urine  being  attended  with  a  copious  precipitation  of  the 
phosphates.  Mental  work  increases  the  amount  of  phosphoric  acid  ex- 
creted, a  condition  caused  by  increased  metabolism  of  the  nervous  tissue. 

Sulphuric  acid  in  combination  with  sodium  and  potassium  constitutes  the 
sulphates,  of  which  about  thirty  grains  are  excreted  daily.  Sulphuric  acid 
results  largely  from  the  decomposition  of  albuminous  food  and  from  in- 
creased destruction  of  animal  tissues. 

The  gases  of  urine  are  carbonic  acid  and  nitrogen. 

Mechanism  of  Urinary  Secretion. — As  the  kidney  anatomically  pre- 
sents an  apparatus  for  filtration  (the  Malpighian  bodies)  and  an  apparatus 
for  secretion  (the  epithelial  cells  of  the  urinary  tubules),  it  might  be  inferred 
that  the  elimination  of  the  constituents  of  the  urine  is  accomplished  by 
the  twofold  process  of  filtration  and  secretion  ;  that  the  water  and  highly 
diffusible  inorganic  salts  simply  pass  by  diffusion  through  the  walls  of  the 
blood-vessels  of  the  glomerulus  into  the  capsule  of  Miiller,  while  the  urea 
and  remaining  organic  constituents  are  removed  by  true  secretory  action  of 
the  renal  epithelium.  Modern  experimentation  supports  this  view  of  renal 
action. 


LIVER.  163 

The  secretion  of  urine  is,  therefore,  partly  physical  and  partly  vital. 

The  filtration  of  urinary  constituents  from  the  glomerulus  into  Midler's 
capsule  depends  largely  upon  the  blood -pressure  and  the  rapidity  of  blood 
flow  in  the  renal  artery  and  glomerulus.  Among  the  influences  which 
increase  the  pressure  and  velocity  may  be  mentioned  increased  frequency 
and  force  of  the  heart's  action,  contraction  of  the  capillary  vessels  of  the 
body  generally,  dilatation  of  the  renal  artery,  and  increase  in  the  volume 
of  the  blood. 

The  reverse  conditions  lower  the  blood -pressure  and  diminish  the  secre- 
tion of  urine. 

The  fact  that  organic  matters  are  eliminated  by  the  secretory  activity  of  the 
renal  epithelium  seems  to  be  well  established  by  modern  experiments. 
These  substances,  removed  from  the  blood  in  the  secondary  capillary  plexus 
of  blood-vessels,  by  a  true  selective  action  of  the  epithelium,  are  dissolved 
and  washed  toward  the  pelves  by  the  liquid  coming  from  the  capsules. 

The  blood-supply  to  the  kidney  is  regulated  by  the  nervous  system.  If 
the  renal  nerves  be  divided,  the  renal  artery  dilates  and  a  copious  flow  of 
urine  takes  place.  If  the  peripheral  ends  of  the  same  nerves  be  stimulated, 
the  artery  contracts  and  the  urinary  flow  ceases.  The  same  is  true  of  the 
splanchnic  nerves,  through  which  the  vaso-motor  nerves  coming  from  the 
medulla  oblongata  and  spinal  cord  pass  to  the  renal  plexus. 


LIVER. 

The  liver  is  a  highly  vascular,  conglomerate  gland,  appended  to  the 
alimentary  canal.  It  is  the  largest  gland  in  the  body,  weighing  about  four 
and  one  half  pounds  ;  it  is  situated  in  the  right  hypochondriac  region,  and 
is  retained  in  position  by  five  ligaments,  four  of  which  are  formed  by  dupli- 
catures  of  the  peritoneal  investment. 

The  proper  coat  of  the  liver  is  a  thin  but  firm  fibrous  membrane,  closely 
adherent  to  the  surface  of  the  organ,  which  it  penetrates  at  the  transverse 
fissure,  and  follows  the  vessels  in  their  ramifications  through  its  substance, 
constituting  Glisson 's  capsule. 

Structure  of  the  Liver. — The  liver  is  made  up  of  a  large  number  of 
small  bodies  (the  lobmes),  rounded  or  ovoid  in  shape,  measuring  ^  of  an 
inch  in  diameter,  separated  by  a  space  in  which  are  situated  blood-vessels, 
nerves,  hepatic  ducts,  and  lymphatics. 


164  HUMAN   PHYSIOLOGY. 

The  lobules  are  composed  of  cells,  which,  when  examined  microscop- 
ically, exhibit  a  rounded  or  polygonal  shape,  and  measure,  on  the  average, 
toVtt  °f  an  *ncn  m  diameter  ;  they  possess  one,  and  sometimes  two,  nuclei ; 
they  also  contain  globules  of  fat,  pigment  matter,  and  animal  starch.  The 
cells  constitute  the  secreting  structure  of  the  liver,  and  are  the  true  hepatic 
cells. 

The  blood-vessels  which  enter  the  liver  are  : 

1.  The  portal  vein,  made  up  of  the  gastric,  splenic,  and  superior  and  infe- 
rior mesenteric  veins. 

2.  The  hepatic  artery,  a  branch  of  the  celiac  axis. 

Both  the  portal  vein  and  the  hepatic  artery  are  invested  by  a  sheath  of 
areolar  tissue. 

The  vessels  which  leave  the  liver  are  the  hepatic  veins,  originating  in  its 
interior,  collecting  the  blood  distributed  by  the  portal  vein  and  hepatic 
artery,  and  conducting  it  to  the  ascending  vena  cava. 

Distribution  of  Vessels. — The  portal 'vein  and  the  hepatic  artery,  upon 
entering  the  liver,  penetrate  its  substance,,  divide  into  smaller  and  smaller 
branches,  occupy  the  spaces  between  the  lobules,  completely  surrounding 
and  limiting  them,  and  constitute  the  interlobular  vessels.  The  hepatic 
artery,  in  its  course,  gives  off  branches  to  the  walls  of  the  portal  vein  and 
Glisson's  capsule,  and  finally  empties  into  the  small  branches  of  the  portal 
vein  in  the  interlobular  spaces. 

The  interlobular  vessels  form  a  rich  plexus  around  the  lobules,  from 
which  branches  pass  to  neighboring  lobules  and  enter  their  substance, 
where  they  form  a  very  fine  network  of  capillary  vessels,  ramifying  over 
the  hepatic  cells,  in  which  the  various  functions  of  the  liver  are  performed. 
The  blood  is  then  collected  by  small  veins,  converging  toward  the  center 
of  the  lobule,  to  form  the  intralobular  vein,  which  runs  through  its  long 
axis  and  empties  into  the  sublobular  vein.  The  hepatic  veins  are  formed 
by  the  union  of  the  sublobular  veins,  and  carry  the  blood  to  the  ascending 
vena  cava  ;  their  walls  are  thin  and  adherent  to  the  substance  of  the  hepatic 
tissue. 

The  hepatic  ducts  or  bile  capillaries  originate  within  the  lobules, 
in  a  very  fine  plexus  lying  between  the  hepatic  cells  ;  whether  the  smallest 
vessels  have  distinct  membranous  walls,  or  whether  they  originate  in  the 
spaces  between  the  cells  by  open  orifices,  has  not  been  satisfactorily  deter- 
mined. 

The  bile-channels  empty  into  the  interlobular  ducts,  which  measure  about 
Wfftf  °f  an  mcn  *n  diameter,  and  are  composed  of  a  thin,  homogeneous 
membrane  lined  by  flattened  epithelial  cells. 


LIVER.  165 

As  the  interlobular  bile-ducts  unite  to  form  large  trunks,  they  receive 
an  external  coat  of  fibrous  tissue,  which  strengthens  their  walls;  they 
finally  unite  to  form  one  large  duct  (the  hepatic  duct),  which  joins  the 
cystic  duct ;  the  union  of  the  two  forms  the  ductus  communis  choledochus, 
which  is  about  three  inches  in  length,  the  size  of  a  goose-quill,  and  opens 
into  the  duodenum. 

The  gall-bladder  is  a  pear-shaped  sac,  about  four  inches  in  length, 
situated  in  a  fossa  on  the  under  surface  of  the  liver.  It  is  a  reservoir  for 
the  bile,  and  is  capable  of  holding  about  one  ounce  and  a  half  of  fluid.  It 
is  composed  of  three  coats  : 

1.  Serous,  a  reflection  of  the  peritoneum. 

2.  Fibrous  and  muscular.  • 

3.  Mucous. 

Functions  of  the  Liver. — The  liver  is  a  complex  organ  having  a 
variety  of  relations  to  the  general  processes  of  the  body.  While  its  physio- 
logic actions  are  not  yet  wholly  understood,  it  may  be  said  that  it — 

1.  Secretes  bile. 

2.  Forms  glycogen. 

3.  Assists  in  the  formation  of  urea  and  allied  products. 

4.  Modifies  the  composition  of  the  blood  as  it  passes  through  it. 

The  Secretion  of  Bile. — The  characteristic  constituents  of  the  bile  do 
not  preexist  in  the  blood,  but  are  formed  in  the  interior  of  the  liver 
cells  of  materials  derived  from  the  venous  and  arterial  blood.  The 
hepatic  cells,  absorbing  these  materials,  elaborate  them  into  bile- elements, 
and  in  so  doing  undergo  histologic  changes  similar  to  those  exhibited  by 
other  secretory  glands.  The  bile  once  formed,  it  passes  into  the  mouths 
of  the  bile  capillaries,  near  the  periphery  of  the  lobules.  Under  the  influ- 
ence of  the  vis  a  tergo  of  the  new-formed  bile  it  flows  from  the  smaller 
into  the  larger  bile-ducts,  and  finally  empties  into  the  intestine,  or  is  regur- 
gitated into  the  gall-bladder,  where  it  is  stored  up  until  it  is  required  for 
the  digestive  process  in  the  small  intestine.  The  study  of  the  secretion  of 
bile  by  means  of  biliary  fistulse  reveals  the  fact  that  the  secretion  is  contin- 
uous and  not  intermittent ;  that  the  hepatic  cells  are  constantly  pouring 
bile  into  the  ducts,  which  convey  it  into  the  gall-bladder.  As  this  fluid  is 
required  only  during  intestinal  digestion,  it  is  only  then  that  the  walls  of 
the  gall-bladder  contract  and  discharge  it  into  the  intestine. 

The  flow  of  bile  from  the  liver  cells  into  the  gall-bladder  is  accomplished 
by  the  inspiratory  movements  of  the  diaphragm,  and  by  the  contraction  of 
the  muscle-fibers  of  the  biliary  ducts,  as  well  as  the  vis  a  tergo  of  new- 


166  HUMAN    PHYSIOLOGY.     ' 

formed  bile.  Any  obstacle  to  the  outflow  of  bile  into  the  intestine  leaps 
to  an  accumulation  within  the  bile-ducts.  The  pressure  within  the  ducts 
increasing  beyond  that  of  the  blood  within  the  capillaries,  a  reabsorption 
of  biliary  matters  by  the  lymphatics  takes  place,  giving  rise  to  the  phe- 
nomena of  jaundice. 

The  bile  is  both  a  secretion  and  an  excretion  ;  it  contains  new  constit- 
uents, which  are  formed  only  in  the  substance  of  the  liver,  and  are  destined 
to  play  an  important  part  ultimately  in  nutrition  ;  it  contains  also  waste 
ingredients,  which  are  discharged  into  the  intestinal  canal  and  eliminated 
from  the  body. 

Glycogenic  Function. — In  addition  to  the  preceding  function,  Ber- 
nard, in  1848,  demonstrated  the  fact  that  the  liver,  during  life,  normally 
produces  a  sugar-forming  substance,  analogous  in  its  chemic  composition  to 
starch,  which  he  terms  glycogen  ;  also  that,  when  the  liver  is  removed  from 
the  body,  and  its  blood-vessels  are  thoroughly  washed  out,  after  a  few  hours 
sugar  again  makes  its  appearance  in  abundance. 

It  can  be  shown  to  exist  in  the  blood  of  the  hepatic  vein  as  well  as  in  a 
decoction  of  the  liver  substance  by  means  of  either  Trommer's  or  Fehling's 
test,  even  when  the  blood  of  the  portal  vein  does  not  contain  a  trace  of 
sugar. 

Origin  and  Destination  of  Glycogen. — Glycogen  appears  to  be 
formed  de  novo  in  the  liver  cells,  from  materials  derived  from  the  food, 
whether  the  diet  be  animal  or  vegetable,  though  a  larger  percentage  is  formed 
when  the  animal  is  fed  on  starchy  and  saccharin  than  when  fed  on  animal 
food.  The  glucose,  which  is  one  of  the  products  of  digestion,  is  absorbed 
by  the  blood-vessels  and  carried  directly  into  the  liver  ;  as  it  does  not 
appear  in  the  urine,  as  it  would  if  injected  at  once  into  the  general  circu- 
lation, it  is  probable  that  it  is  detained  in  the  liver,  dehydrated,  and  stored 
up  as  glycogen.     The  change  is  shown  by  the  following  formula  : 

C6H12°6  —  H2°  =  C6H10°5- 
Glucose.         Water.       Glycogen. 

The  glycogen  thus  formed  is  stored  up  in  the  hepatic  cells  for  the  future 
requirements  of  the  system.  When  it  is  carried  from  the  liver,  it  is  again 
transformed  into  glucose  by  the  agency  of  a  ferment.  Glycogen  does  not 
undergo  oxidation  in  the  blood  ;  this  process  takes  place  in  the  tissues, 
particularly  in  the  muscles,  where  it  generates  heat  and  contributes  to  the 
development  of  muscular  force. 


LIVER.  167 

Glycogen,  when  obtained  from  the  liver,  is  an  amorphous,  starch-like 
substance,  of  a  white  color,  tasteless  and  colorless,  and  soluble  in  water  ; 
by  boiling  with  dilute  acids,  or  subjected  to  the  action  of  an  animal  ferment, 
it  is  easily  converted  into  dextrose.  When  an  excess  of  sugar  is  generated 
by  the  liver,  dextrose  can  be  found  not  only  in  the  blood  of  the  hepatic  vein, 
but  also  in  other  portions  of  the  body  ;  under  these  circumstances  it  is  elimi- 
nated by  the  kidneys,  appearing  in  the  urine,  constituting  the  condition  of 
glycosuria . 

Formation  of  Urea. — The  liver  is  now  regarded  by  many  physiolo- 
gists as  the  principal  organ  concerned  in  urea  formation.  The  liver 
normally  contains  a  certain  amount  of  urea  ;  and  if  blood  be  passed 
through  the  excised  liver  of  an  animal  which  has  been  in  full  digestion 
when  killed,  a  large  amount  of  urea  is  obtained.  The  clinical  evidence 
proves  that  in  destructive  diseases  of  the  liver  substance  there  is  at  once  a 
falling-off  in  urea  elimination.  Various  drugs  which  stimulate  liver  action 
increase  the  urea  in  the  urine. 

Elaboration  of  Blood. — Besides  the  capability  of  secreting  bile,  the  liver 
possesses  the  property  of  so  acting  upon  and  modifying  the  chemic  compo- 
sition of  the  products  of  digestion  as  they  traverse  its  substance  that  they  are 
readily  assimilated  by  the  blood,  and  are  transformed  into  materials  capa- 
ble of  being  converted  into  the  elements  of  the  blood  and  into  solid  tissues. 

The  albuminous  principles  particularly  require  the  modifying  influence  of 
the  liver  ;  for  if  they  are  removed  from  the  portal  vein  and  introduced  into 
the  jugular  vein,  they  are  at  once  removed  from  the  blood  by  the  action  of 
the  kidneys. 

The  blood  of  the  hepatic  vein  differs  from  the  blood  of  the  portal  vein 
in  being  richer  in  blood-corpuscles,  both  red  and  white  ;  its  plasma  is  more 
dense,  containing  a  smaller  percentage  of  water  and  a  greater  amount  of 
solid  constituents,  but  no  fibrin  ;  its  serum  contains  less  albumin,  fats,  and 
salts,  but  its  sugar  is  increased. 

Influence  of  the  Nervous  System. — The  nervous  system  directly 
controls  the  functional  activity  of  the  liver,  and  more  especially  its  glyco- 
genic function.  It  was  discovered  by  Bernard  that  puncture  of  the  medulla 
oblongata  is  followed  by  so  enormous  a  production  of  sugar  that  it  is  at 
once  excreted  by  the  kidneys,  giving  rise  to  diabetic  or  saccharine  urine. 
This  part  of  the  medulla  is,  however,  the  vaso-motor  center  for  the  blood- 
vessels of  the  liver.  Destruction  of  this  center,  or  injury  to  the  vaso-motor 
nerves  emanating  from  it  in  any  part  of  their  course,  is  followed  at  once  by 
dilatation  of  the  hepatic  blood-vessels,  slowing  of  the  blood- current,  a  pro- 


168  HUMAN    FHYSIOLOGY. 

found  disturbance  of  the  normal  relation  existing  between  the  blood  and 
liver-cells,  and  a  production  of  sugar.  Many  of  the  hepatic  vaso-motor 
nerves  may  be  traced  down  the  cord  as  far  as  the  lumbar  region,  while 
others  leave  the  cord  high  up  in  the  neck  and  enter  the  cervical  ganglia  of 
the  sympathetic,  and  so  reach  the  liver.  Injury  to  the  sympathetic  ganglia 
is  often  followed  by  diabetes.  Peripheral  stimulation  of  various  nerves,  — 
e.  g.,  sciatic,  pneumogastric,  depressor  nerve,  — as  well  as  the  direct  action 
of  many  drugs,  impair  or  depress  the  hepatic  vaso-motor  center  and  so  give 
rise  to  diabetes. 


SKIN. 

The  skin,  the  external  investment  of  the  body,  is  a  most  complex  and 
important  structure,  serving  — 

1.  As  a. protective  covering. 

2.  As  an  organ  for  tactile  sensibility. 

3.  As  an  organ  for  the  elimination  of  excre??ientitious  matters. 

The  amount  of  skin  investing  the  body  of  a  man  of  average  size  is 
about  twenty  feet,  and  varies  in  thickness,  in  different  situations,  from  \  to 
Ti^  of  an  inch. 

The  skin  consists  of  two  principal  layers  —  viz.,  a  deeper  portion,  the 
corium,  and  a  superficial  portion,  the  epider?nis. 

The  corium,  or  cutis  vera,  may  be  subdivided  into  a  reticulated  and  a 
papillary  layer.  The  former  is  composed  of  white  fibrous  tissue,  non- 
striated  muscle-fibers,  and  elastic  tissue,  interwoven  in  every  direction, 
forming  an  areolar  network,  in  the  meshes  of  which  are  deposited  masses 
of  fat,  and  a  structureless,  amorphous  matter ;  the  latter  is  formed  mainly 
of  club-shaped  elevations  or  projections  of  the  amorphous  matter,  consti- 
tuting the  papillce  ;  they  are  most  abundant  and  well  developed  upon  the 
palms  of  the  hands  and  upon  the  soles  of  the  feet ;  they  average  T^  of  an 
inch  in  length,  and  may  be  simple  or  compound  ;  they  are  well  supplied 
with  nerves,  blood-vessels,  and  lymphatics. 

The  epidermis,  or  scarf  skin,  is  an  extravascular  structure,  a  product 
of  the  true  skin,  and  is  composed  of  several  layers  of  cells.  It  may  be 
divided  into  two  layers  :  the  rete  mucosum,  or  the  Malpighian  layer,  and 
the  horny  or  corneous. 

The  former  is  closely  adherent  to  the  papillary  layer  of  the  true  skin, 


SKIN.  169 

and  is  composed  of  large,  nucleated  cells,  the  lowest  layer  of  which,  the 
"prickle  cells,"  contains  pigment-granules,  which  give  to  the  skin  its 
varying  tints  in  different  individuals  and  in  different  races  of  men  ;  the 
more  superficial  cells  are  large,  colorless,  and  semi-transparent.  The  latter, 
the  corneous  layer,  is  composed  of  flattened  cells,  which,  from  their 
exposure  to  the  atmosphere,  are  hard  and  horny  in  texture  ;  it  varies  in 
thickness  from  \  of  an  inch  on  the  palms  of  the  hands  and  soles  of  the  feet 
to  j^-q  of  an  inch  in  the  external  auditory  canal. 


APPENDAGES  OF  THE  SKIN. 

Hairs  are  found  in  almost  all  portions  of  the  body,  and  can  be  divided 
into  — 

1.  Long,  soft  hairs,  on  the  head. 

2.  Short,  stiff  hairs,  along  the  edges  of  the  eyelids  and  nostrils. 

3.  Soft,  downy  hairs  on  the  general  cutaneous  surface. 

They  consist  of  a  root  and  a  shaft.  The  latter  is  oval  in  shape  and 
about  ¥^-j5-  of  an  inch  in  diameter ;  it  consists  of  fibrous  tissue,  covered 
externally  by  a  layer  of  imbricated  cells,  and  internally  by  cells  containing 
granular  and  pigment  material. 

The  root  of  the  hair  is  embedded  in  the  hair- follicle,  formed  by  a  tubular 
depression  of  the  skin,  extending  nearly  through  to  the  subcutaneous  tissue  ; 
its  walls  are  formed  by  the  layers  of  the  corium,  covered  by  epidermic  cells. 
At  the  bottom  of  the  follicle  is  a  papillary  projection  of  amorphous  matter, 
corresponding  to  a  papilla  of  the  true  skin,  containing  blood-vessels  and 
nerves,  upon  which  the  hair-root  rests.  The  investments  of  the  hair-roots 
are  formed  of  epithelial  cells,  constituting  the  internal  and  external  root- 
sheaths. 

The  hair  protects  the  head  from  the  heat  of  the  sun  and  from  the  cold, 
retains  the  heat  of  the  body,  prevents  the  entrance  of  foreign  matter  into 
the  lungs,  nose,  ears,  etc.  The  color  is  due  to  pigment  matter.  In  old 
age  the  hair  becomes  more  or  less  whitened. 

The  sebaceous  glands,  embedded  in  the  true  skin,  are  simple  and 
compound  racemose  glands,  opening,  by  a  common  excretory  duct,  upon 
the  surface  of  the  epidermis  or  into  the  hair-follicle.  They  are  found  in 
all  portions  of  the  body,  most  abundantly  in  the  face,  and  are  formed  by 
a  delicate,  structureless  membrane,  lined  by  flattened  polyhedral  cells.  The 
sebaceous  glands  secrete  a  peculiar  oily  matter  (the  sebum),  by  which  the 
12 


170  HUMAN    PHYSIOLOGY. 

skin  is  lubricated  and  the  hairs  are  softened ;  it  is  quite  abundant  in  the 
region  of  the  nose  and  forehead,  which  often  presents  a  greasy,  glistening 
appearance ;  it  consists  of  water,  mineral  salts,  fatty  globules,  and  epithe- 
lial cells. 

The  vernix  caseosa,  which  frequently  covers  the  surface  of  the  fetus  at 
birth,  consists  of  the  residue  of  the  sebaceous  matter,  containing  epithelial 
cells  and  fatty  matters  ;  it  seems  to  keep  the  skin  soft  and  supple,  and 
guards  it  from  the  effects  of  the  long- continued  action  of  the  amniotic  water. 

The  sudoriparous  glands  excrete  the  sweat.  They  consist  of  a  mass 
or  coil  of  a  tubular  gland  duct,  situated  in  the  derma  and  in  the  subcutane- 
ous tissue,  average  y1^  of  an  inch  in  diameter,  and  are  surrounded  by 
a  rich  plexus  of  capillary  blood-vessels.  From  this  coil  the  duct  passes 
in  a  straight  direction  up  through  the  skin  to  the  epidermis,  where  it 
makes  a  few  spiral  turns  and  opens  obliquely  upon  the  surface.  The 
sweat-glands  consist  of  a  delicate  homogeneous  membrane  lined  by  epi- 
thelial cells,  whose  function  is  to  extract  from  the  blood  the  elements 
existing  in  the  perspiration. 

The  glands  are  very  abundant  all  over  the  cutaneous  surface — as  many  at 
3528  to  the  square  inch,  according  to  Erasmus  Wilson. 

The  perspiration  is  an  excrementitious  fluid,  clear,  colorless,  almost 
odorless,  slightly  acid  in  reaction,  with  a  specific  gravity  of  1003  to  1004. 

The  total  quantity  of  perspiration  excreted  daily  has  been  estimated  at 
about  two  pounds,  though  the  amount  varies  with  the  nature  of  the  food 
and  drink,  exercise,  external  temperature,  season,  etc. 

The  elimination  of  the  sweat  is  not  intermittent,  but  continuous ;  it 
takes  place  so  gradually  that  as  fast  as  it  is  formed  it  passes  off  by 
evaporation  as  insensible  perspiration.  Under  exposure  to  great  heat  and 
exercise  the  evaporation  is  not  sufficiently  rapid,  and  it  appears  as  sensible 
perspiration. 

COMPOSITION  OF  SWEAT. 

Water, 995-573 

Urea, 0.043 

Fatty  matters,       0.014 

Alkaline  lactates, °-3l7 

Alkaline   sudorates, 1. 562 

Inorganic  salts, 2-49l 

1,000.000 
Urea  is  a  constant  ingredient. 

Carbonic  acid  is  also  exhaled  from  the  skin,  the  amount  being  about  ^^ 
of  that  from  the  lungs. 


CEREBROSPINAL   AXIS.  171 

Perspiration  regulates  the  temperature  and  removes  waste  matters  from 
the  blood  ;  it  is  so  important  that  if  elimination  be  prevented,  death  occurs 
in  a  short  time. 

Influence  of  the  Nervous  System. — The  secretion  of  sweat  is  regu- 
lated by  the  nervous  system.  Here,  as  in  the  secreting  glands,  the  fluid  is 
formed  from  material  in  the  lymph-spaces  surrounding  the  gland.  Two 
sets  of  nerves  are  concerned — viz. ,  vaso-motor,  regulating  the  blood-supply  ; 
and  secretory,  stimulating  the  activities  of  the  gland  cells.  Generally  the 
two  conditions,  increased  blood  flow  and  increased  glandular  action,  coexist. 
At  times  profuse  clammy  perspiration  occurs,  with  diminished  blood  flow. 

The  dominating  sweat-center  is  located  in  the  medulla,  though  subordi- 
nate centers  are  present  in  the  cord.  The  secretory  fibers  reach  the  perspi- 
ratory glands  of  the  head  and  face  through  the  cervical  sympathetic  ;  of 
the  arms,  through  the  thoracic  sympathetic,  ulnar,  and  radial  nerves  ;  of  the 
leg,  through  the  abdominal  sympathetic  and  sciatic  nerves. 

The  sweat-center  is  excited  to  action  by  mental  emotions,  increased  tem- 
perature of  blood  circulating  in  the  medulla  and  cord,  increased  venosity 
of  blood,  many  drugs,  rise  of  external  temperature,  exercise,  etc. 


CEREBRO-SPINAL  AXIS. 

The  cerebro-spinal  axis  consists  of  the  spinal  cord,  medulla  oblongata, 
pons  Varolii,  cerebellum,  and  cerebrum,  exclusive  of  the  spinal  and 
cranial  nerves.  It  is  contained  within  the  cavities  of  the  cranium  and 
spinal  column,  and  surrounded  by  three  membranes, — the  dura  mater, 
arachnoid,  and  pia  mater, — which  protect  it  from  injury  and  supply  it  with 
blood-vessels. 

MEMBRANES. 

The  dura  mater,  the  outermost  of  the  three,  is  a  tough  membrane, 
composed  of  white  fibrous  tissue  arranged  in  bundles,  which  interlace  in 
every  direction.  In  the  cranial  cavity  it  lines  the  inner  surface  of  the 
bones,  and  is  attached  to  the  edge  of  the  foramen  magnum ;  it  sends  proc- 
esses inward,  forming  the  falx  cerebri,  falx  cerebelli,  and  tentorium  cere- 
belli,  supporting  and  protecting  parts  of  the  brain.  In  the  spinal  canal  it 
loosely  invests  the  cord,  and  is  separated  from  the  walls  of  the  canal  by 
areolar  tissue. 


172  HUMAN    PHYSIOLOGY. 

The  arachnoid,  the  middle  membrane,  is  a  delicate  serous  structure 
which  envelops  the  brain  and  cord,  forming  the  visceral  layer,  and  is  then 
reflected  to  the  inner  surface  of  the  dura  mater,  forming  the  parietal  layer. 
Between  the  two  layers  there  is  a  small  quantity  of  fluid,  which  prevents 
friction  by  lubricating  the  two  surfaces. 

The  pia  mater,  the  innermost  of  the  three,  composed  of  areolar 
tissue  and  blood-vessels,  covers  the  entire  surface  of  the  brain  and  cord, 
to  which  it  is  closely  adherent,  dipping  down  between  the  convolutions 
and  fissures.  It  is  exceedingly  vascular,  sending  small  blood-vessels  some 
distance  into  the  brain  and  cord. 

The  cerebro- spinal  fluid  occupies  the  subarachnoid  space  and  the 
general  ventricular  cavities  of  the  brain,  which  communicate  by  an  opening 
(the  foramen  of  Magendie)  in  the  pia  mater,  at  the  lower  portion  of  the 
fourth  ventricle.  This  fluid  is  clear,  transparent,  alkaline,  possesses  a  salty 
taste,  and  has  a  low  specific  gravity ;  it  is  composed  largely  of  water,  and 
there  are  traces  of  albumin,  glucose,  and  mineral  salts.  It  is  secreted  by 
the  pia  mater  ;  the  quantity  is  estimated  at  from  two  to  four  fluidounces. 

The  function  of  the  cerebro- spinal  fluid  is  to  protect  the  brain  and  cord 
by  preventing  concussion  from  without ;  as  it  is  easily  displaced  into  the 
spinal  canal,  it  prevents  undue  pressure  and  insufficiency  of  blood  to  the 
brain. 


SPINAL  CORD. 

The  spinal  cord  varies  from  sixteen  to  eighteen  inches  in  length  ;  it  is 
]/z  of  an  inch  in  thickness,  weighs  \y2  ounces,  and  extends  from  the  atlas 
to  the  second  lumbar  vertebra,  terminating  in  the  filum  terminate.  It  is 
cylindric  in  shape,  and  presents  an  enlargement  in  the  lower  cervical  and 
lower  dorsal  regions,  corresponding  to  the  origin  of  those  nerves  which  are 
distributed  to  the  upper  and  lower  extremities.  The  cord  is  divided  into 
two  lateral  halves  by  the  anterior  and  posterior  fissures.  It  is  composed  of 
both  white  or  fibrous  and  gray  or  vesicular  matter,  the  former  occupying 
the  exterior  of  the  cord,  the  latter  the  interior,  where  it  is  arranged  in  the 
form  of  two  crescents,  one  in  each  lateral  half,  united  by  the  central  mass, 
the  gray  commissure  ;  the  white  matter  being  united  in  front  by  the  white 
commissure. 

Structure  of  the  Gray  Matter. — The  gray  matter  is  arranged  in  the 
form  of  two  crescents,  united  by  a  commissural  band,  forming  a  figure 


SPINAL   CORD. 


173 


a 


resembling  the  letter  H.  Each  crescent  presents  an  anterior  and  a  posterior 
horn.  The  center  of  the  commissure  presents  a  canal  which  extends  from 
the  fourth  ventricle  downward  to  the  filum  terminale.  The  anterior  horn 
is  short  and  broad  and  does  not  extend  to  the  surface.  The  posterior  horn 
is  narrow  and  elongated  and  extends  quite  to  the  surface.  It  is  covered 
and  capped  by  the  substantia  gelatinosa.  The  gray  matter  consists  pri- 
marily of  a  framework  of  fine  connective  tissue,  supporting  blood-vessels, 
lymphatics,  medullated  and  non-medullated  nerve-fibers,  and  groups  of 
nerve-cells. 

The  nerve-cells  are  arranged  in  groups,  which  extend  for  some  distance 
throughout  the  cord,  forming 
columns  more  or  less  continu- 
ous. The  first  group  is  situ- 
ated in  the  anterior  horn,  the 
cells  of  which  are  large,  multi- 
polar, and  connected  with  the 
anterior  roots  of  the  spinal 
nerves.  The  second  group  is 
situated  in  the  posterior  horn, 
the  cells  of  which  are  spindle- 
shaped,  and  from  their  relation 
to  the  posterior  roots  are  sup- 
posed to  be  sensory  in  function. 
The  third  group  is  situated  in 
the  lateral  aspect  of  the  gray 
matter,  and  is  quite  separate 
and  distinct,  except  in  the  lum- 
bar and  cervical  enlargements, 
where  it  blends  with  those  of 
the  anterior  horn.  A  fourth 
group  is    situated  at   the   inner 

base  of  the  posterior  horn  ;  it  begins  about  the  seventh  or  eighth  cervical 
nerve  and  extends  downward  to  the  second  or  third  lumbar,  being  most 
prominent  in  the  dorsal  region.  This  column  is  known  as  Clark's  vesicular 
column. 

Structure  of  the  White  Matter. — The  white  matter  surrounding  each 
lateral  half  of  the  cord  is  made  up  of  nerve-fibers,  some  of  which  are 
continuations  of  the  nerves  which  enter  the  cord,  while  others  are  derived 
from  different  sources.     It  is  subdivided  into — 


Fig.  21. — Scheme  of  the  Conducting 
Path  in  the  Spinal  Cord  at  the 
Third  Dorsal  Nerve. — {Landois  ) 

The  black  part  is  the  gray  matter,  v.  Ante- 
rior, hw,  posterior,  root.  a.  Direct,  and 
g,  g,  crossed,  pyramidal  tracts.  b.  An- 
terior column,  ground  bundle.  c.  Goll's 
column,  d.  Postero-external  column,  e,  e, 
and  f,  f.  Mixed  lateral  paths,  h,  h.  Direct 
cerebellar  tracts. 


174  HUMAN    PHYSIOLOGY. 

1.  An  anterior  column,  comprising  that  portion  between  the  anterior  roots 
and  the  anterior  fissure,  which  is  again  subdivided  into  two  parts  : 

(a)  An  inner  portion,  bordering  the  anterior  median  fissure,  the  direct 
pyramidal  tract,  or  column  of  Tiirck  ;  it  contains  motor  fibers  which 
do  not  decussate,  and  which  extend  as  far  down  as  the  middle  of 
the  dorsal  region. 

(b)  An  otder  portion,  surrounding  the  anterior  cornua,  known  as  the 
a?iterior  root  zone,  composed  of  short,  longitudinal  fibers  which 
serve  to  connect  different  segments  of  the  spinal  cord. 

2.  A  lateral  column,  the  portion  between  the  anterior  and  posterior  roots, 
which  is  divisible  into — 

(a)  The  crossed  pyramidal  tract,  occupying  the  posterior  portion  of 
the  lateral  column,  and  containing  all  those  fibers  of  the  motor  tract 
which  have  decussated  at  the  medulla  oblongata  ;  it  is  composed  of 
longitudinally  running  fibers,  which  are  connected  with  the  multi- 
polar nerve-cells  of  the  anterior  cornua. 

(b)  The  direct  cerebellar  tract,  situated  upon  the  surface  of  the  lat- 
eral column,  consisting  of  longitudinal  fibers  which  terminate  in  the 
cerebellum  ;  it  first  appears  in  the  lumbar  region,  and  increases  in 
thickness  as  it  passes  upward. 

(c)  The  anterior  tract,  lying  just  posterior  to  the  anterior  cornua. 

3.  A  posterior  column,  the  portion  included  between  the  posterior  roots  and 
the  posterior  fissure,  also  divisible  into  two  portions  : 

(a)  An  inner  portion,  the  poster o-internal  column,  or  the  column  of 
Goll,  bordering  the  posterior  median  fissure,  and 

(b)  An  external  portion,  the  postero-extemal  column,  the  column  of 
Burdach,  lying  just  behind  the  posterior  roots. 

The  two  portions  of  the  posterior  column  are  composed  of  long  and  short 
commissural  fibers,  which  connect  different  segments  of  the  spinal  cord. 


SPINAL  NERVES. 

Origin. — The  spinal  nerves  are  thirty-one  in  number  on  each  side  of  the 
spinal  cord,  and  arise  by  two  roots,  an  anterior  and  a  posterior,  from  the 
anterior  and  posterior  aspect  of  the  cord,  respectively.  The.  posterior  roots 
present,  near  their  emergence  from  the  cord,  a  small  ganglionic  enlarge- 
ment. Outside  of  the  spinal  canal  the  two  roots  unite  to  form  a  main  trunk, 
which  is  ultimately  distributed  to  the  skin,  muscles,  and  viscera. 

For  the  functions  of  the  roots  of  the  spinal  nerves,  see  page  77. 


SPINAL   CORD.  175 


COURSE  OF  THE  ANTERIOR  AND  POSTERIOR  ROOTS. 

The  anterior  roots  pass  through  the  anterior  columns,  horizontally,  in 
straight  and  distinct  bundles,  and  enter  the  anterior  cornua,  where  they 
diverge  in  four  directions  : 

1.  Many  become  connected  with  the  prolongations  of  the  multipolar  nerve- 
cells. 

2.  Others  leave  the  gray  matter,  pass  through  the  anterior  white  commis- 
sure, and  enter  the  anterior  columns  of  the  opposite  side. 

3.  A  considerable  number  enter  the  lateral  columns  of  the  same  side, 
through  which  they  pass  to  the  medulla  oblongata,  where  they  decussate 
and  finally  terminate  in  the  corf -us  striatum  of  the  opposite  side. 

4.  Others  traverse  the  gray  matter  horizontally,  and  come  into  relation  with 
the  cells  of  the  intermediary  lateral  column. 

The  posterior  roots  enter  the  posterior  horns  of  the  gray  matter — 

1.  Through  the  substantia  gelatinosa. 

2.  Through  the  posterior  columns. 

Of  the  former  some  bend  upward  and  downward,  and  become  connected 
with  the  anterior  cornua  ;  others  pass  through  the  posterior  commissure  to 
the  opposite  side  ;  of  the  latter,  fibers  pass  into  the  gray  matter  to  the  poste- 
rior vesicular  columns,  passing  obliquely  through  the  posterior  white  col- 
umns upward  and  downward  for  some  distance,  and  enter  the  gray  matter 
at  different  heights. 

Decussation  of  Motor  and  Sensory  Fibers. — The  motor  fibers, 
which  conduct  volitional  impulses  from  the  brain  outward  to  the  anterior 
cornua,  arise  in  the  motor  centers  of  the  cerebrum  ;  they  then  pass  down- 
ward through  the  corona  radiata,  the  internal  capsule,  the  inferior  portions 
of  the  crura  cerebri,  the  pons  Varolii,  to  the  medulla  oblongata,  where  the 
motor  tract  of  each  side  divides  into  two  portions,  viz.  : 

1.  The  larger,  containing  ninety-one  to  ninety-seven  per  cent,  of  the  fibers, 
which  decussates  at  the  lower  border  of  the  medulla  and  passes  down  in 
the  lateral  column  of  the  opposite  side,  and  constitutes  the  crossed  pyra- 
midal tract. 

2.  The  smaller,  containing  three  to  nine  per  cent,  of  the  fibers,  does  not 
decussate,  but  passes  down  the  anterior  column  of  the  same  side,  and 
constitutes  the  direct  pyramidal  tract,  or  the  column  of  Turck. 

Some  of  the  motor  fibers  of  these  two  tracts,  after  entering  the  anterior 
cornua  of  the  gray  matter,  become  connected  with  the  large  multipolar 


176  HUMAN   PHYSIOLOGY. 

nerve- cells,  while  others  pass  directly  into  the  anterior  roots.  Through  this 
decussation  each  half  of  the  brain  governs  the  muscular  movements  of 
the  opposite  side  of  the  body. 

The  sensory  fibers,  which  convey  to  the  cord  and  brain  the  impression 
made  upon  the  periphery,  pass  into  the  cord  through  the  posterior  roots 
of  spinal  nerves  ;  they  then  diverge  and  enter  the  gray  matter  at  differen 
levels,  and  at  once  decussate,  passing  to  the  opposite  side  of  the  gray 
matter.  The  sensory  tract  passes  upward,  through  the  cord,  the  medulla, 
pons  Varolii,  the  superior  portion  of  the  cruri  cerebri,  the  posterior  third 
of  the  internal  capsule,  to  the  sensory  perceptive  center,  located  in  the 
hippocampus  major  and  uncinate  convolution  (Ferrier).  Through  this  de- 
cussation each  half  of  the  brain  governs  the  sensibility  of  the  opposite  half 
of  the  body. 

Properties  of  the  Spinal  Cord. — Irritation  applied  directly  to  the 
anterolateral  white  columns  produces  muscular  movements,  but  no  pain ; 
they  are,  therefore,  excitable,  but  insensible. 

The  surface  of  the  posterior  columns  is  not  sensitive  to  direct  irritation, 
except  near  the  origin  of  the  posterior  roots.  The  sensibility  is  due,  how- 
ever, not  to  its  own  proper  fibers,  but  to  the  fibers  of'  the  posterior  root, 
which  traverse  it. 

Division  of  the  anterolateral  columns  abolishes  all  power  of  voluntary 
movement  in  the  lower  extremities. 

Division  of  the  posterior  column  impairs  the  power  of  muscular  coordi- 
nation, such  as  is  witnessed  in  locomotor  ataxia. 

The  gray  matter  is  probably  both  insensible  and  inexcitable  under  the 
influence  of  direct  stimulation. 

A  transverse  section  of  one  lateral  half  of  the  cord  produces — 

1.  On  the  same  side,  paralysis  of  voluntary  motion,  a  relative  or  abso- 
lute elevation  of  temperature,  and  an  increased  flow  of  blood  in  the 
paralyzed  parts  ;  hyperesthesia,  for  the  sense  of  contact,  tickling  ,pain, 
and  temperature. 

2.  On  the  opposite  side,  complete  anesthesia  as  regards  contact,  tickling, 
and  temperature  in  the  parts  corresponding  to  those  which  are  paralyzed 
in  the  opposite  side,  with  a  complete  preservation  of  voluntary  power 
and  of  the  muscular  sense. 

A  vertical  section  through  the  middle  of  the  gray  matter  results  in  the 
loss  of  sensation  on  both  sid^s  of  the  body  below  the  section,  but  no  loss 
of  voluntary  power. 


SPINAL   CORD. 


177 


Fig.  22. — Diagram   showing  the  Course,  through  the   Spinal  Cord,  of  the 
Motor  and  Sensory  Nerve-fibers. 

B  and  B'  represent  the  right  and  left  hemispheres  of  the  brain,  from  which  the  motor 
fibers  take  their  origin,  and  in  which  the  sensory  fibers  terminate.  The  viotor  tract 
from  the  right  side,  i,  passes  down  through  the  crus,  through  the  pons  to  the  medulla 
oblongata,  where  it  divides  into  two  portions  :  (i)  The  larger  portion,  ninety-seven 
per  cent.,  crosses  over  to  the  opposite  side  of  the  cord  and  passes  down  through  the 
lateral  column.  It  gives  off  fibers  at  different  levels,  which  pass  into  the  gray  matter 
and  become  connected  with  the  muscles,  M,  through  the  multipolar  cells.  (2)  The 
smaller  portion,  three  per  cent.,  does  not  cross  over,  but  descends  on  the  same  side 
of  the  cord  in  the  anterior  column  and  supplies  the  muscles,  m.  The  same  is  true 
for  the  motor  tract  for  the  left  hemisphere. 

The  sensory  fibers  from  the  left  side  of  the  body  enter  the  gray  matter  through  the  pos- 
terior roots.  They  then  cross  over  at  once  to  the  opposite  side  of  the  cord  and  ascend 
to  the  hemisphere,  partly  in  the  gray  matter,  partly  in  the  posterior  column.  The 
same  is  true  for  the  sensory  nerves  of  the  right  side  of  the  body. 


178  HUMAN   PHYSIOLOGY. 


FUNCTIONS    OF    THE    SPINAL    CORD. 

i.  As  an  Independent  Nerve  Center. 

The  spinal  cord,  in  virtue  of  its  contained  nerve-cells,  is  capable  of 
transforming  afferent  nerve  impulses  arriving  through  the  afferent  nerves 
into  efferent  impulses,  which  are  reflected  outward  through  efferent  nerves 
to  muscles,  producing  motion ;  to  glands,  exciting  secretion  ;  to  blood- 
vessels, changing  their  caliber.  All  such  actions  taking  place  independent 
of  either  sensation  or  volition  are  termed  reflex  actions.  The  mechanism 
involved  in  every  reflex  action  consists  of  a  sentient  surface,  an  afferent 
nerve,  an  emissive  center,  an  efferent  nerve,  and  a  responsive  organ, 
muscle,  gland,  or  blood-vessel  (see  p.  81). 

The  reflex  excitability  of  the  cord  may  be — 

1.  Increased  by  disease  of  the  lateral  columns,  by  the  administration  of 
strychnin,  and,  in  frogs,  by  a  separation  of  cord  from  the  brain,  the 
latter  apparently  exerting  an  inhibitory  influence  over  the  former  and 
depressing  its  reflex  activity. 

2.  Inhibited  by  destructive  lesion  of  the  cord — e.  g.,  locomotor  ataxia, 
atrophy  of  the  anterior  cornua — the  administration  of  various  drugs,  and, 
in  the  frog,  by  irritation  of  certain  regions  of  the  brain.  When  the 
cerebrum  alone  is  removed  and  the  optic  lobes  are  stimulated,  the  time 
elapsing  between  the  application  of  an  irritant  to  a  sensory  surface  and 
the  resulting  movement  will  be  considerably  prolonged,  the  optic  lobes 
(Setschenow's  center)  apparently  generating  impulses  which,  descend- 
ing the  cord,  retard  its  reflex  movement. 

All  movements  taking  place  through  the  nervous  system" are  of  this  reflex 
character,  and  may  be  divided  into  excito-motor,  sensori-motor,  and  ideo- 
motor. 

Classification  of  Reflex  Movements  (Kiiss). — They  may  be  divided 
into  four  groups,  according  to  the  route  through  which  the  centripetal  and 
centrifugal  impulses  pass  : 

1.  Those  normal  reflex  acts  {e.g. ,  deglutition,  coughing,  sneezing,  walking, 
etc.)  and  pathologic  reflex  acts  (e.g.,  tetanus,  vomiting,  epilepsy)  which 
take  place  both  centripetally  and  centrifugally  through  spinal  nerves. 

2.  Reflex  acts  which  take  place  in  a  centripetal  direction  through  a  cere- 
brospinal sensory  nerve,  and  in  a  centrifugal  direction  through  a  sym- 
pathetic motor  nerve,  usually  a  vaso-motor  nerve — e.  g.,  the  normal  reflex 
acts,  which  give  rise  to  most  of  the  secretions,  pallor  of  the  skin  and 
blushing,  certain  movements  of  the  iris,  certain  modifications  in  the  beat 


SPINAL   CORD.  179 

of  the^heart ;  the  pathologic  reflexes,  which,  on  account  of  the  difficulty 
in  explaining  their  production,  are  termed  metastatic — e.  g.,  ophthalmia, 
coryza,  orchitis,  which  depend  on  a  reflex  hyperemia ;  amaurosis,  par- 
alysis, paraplegia,  etc.,  due  to  a  reflex  anemia. 

3.  Reflex  movements  in  which  the  centripetal  impulse  passes  through  a 
sympathetic  nerve,  and  the  centrifugal  through  a  cerebro-spinal  nerve  ; 
most  of  these  phenomena  are  pathologic — e.  g.,  convulsions  from  intes- 
tinal irritation  produced  by  the  presence  of  worms,  eclampsia,  hysteria, 
etc. 

4.  Reflex  actions  in  which  both  the  centripetal  and  centrifugal  impulses 
pass  through  filaments  of  the  sympathetic  nervous  system — e.  g.,  those 
obscure  reflex  actions  which  preside  over  the  secretions  of  the  intestinal 
fluids,  which  unite  the  phenomena  of  the  generative  organs,  the  dilata- 
tion of  the  pupils  from  intestinal  irritation  (worms),  and  many  path- 
ologic phenomena. 

Laws  of  Reflex  Action  (Pfliiger). 

1.  Law  of  Unilaterality. — If  a  feeble  irritation  be  applied  to  one  or  more 
sensory  nerves,  movement  takes  place  usually  on  one  side  only,  and  that 
the  same  side  as  the  irritation. 

2.  Law  of  Symmetry. — If  the  irritation  becomes  sufficiently  intense,  motor 
reaction  is  manifested,  in  addition,  in  corresponding  muscles  of  the  oppo- 
site side  of  the  body. 

3.  Law  of  Intensity. — Reflex  movements  are  usually  more  intense  on  the 
side  of  the  irritation  ;  at  times  the  movements  of  the  opposite  side  equal 
them  in  intensity,  but  they  are  usually  less  pronounced. 

4.  Law  of  Radiation. — If  the  excitation  still  continues  to  increase,  it  is 
propagated  upward,  and  motor  reaction  takes  place  through  centrifugal 
nerves  coming  from  segments  of  the  cord  higher  up. 

5.  Law  of  Generalization. — When  the  irritation  becomes  very  intense,  it 
is  propagated  in  the  medulla  oblongata ;  motor  reaction  then  becomes 
general,  and  it  is  propagated  up  and  down  the  cord,  so  that  all  the 
muscles  of  the  body  are  thrown  into  action,  the  medulla  oblongata  act- 
ing as  a  focus  whence  radiate  all  reflex  movements. 

Special  Reflex  Movements. 

There  are  a  number  of  reflex  movements  taking  place  through  the  spinal 
cord,  a  study  of  which  enables  the  physician  to  determine  the  condition  of 
its  different  segments.     They  may  be  divided  into — 

1.  Skin  or  superficial,  and 

2.  Tendon  or  deep  reflexes. 


180  HUMAN    PHYSIOLOGY. 

The  skin  reflexes  are  induced  by  irritation  of  the  skin  and  mucous  mem- 
branes— e.  g.,  pricking,  pinching,  scratching,  etc.  The  following  are  the 
principal  skin  reflexes  : 

1.  Plantar  reflex,  consisting  of  contraction  of  the  muscles  of  the  foot, 
induced  by  stimulation  of  the  sole  of  the  foot ;  it  involves  the  integrity 
of  the  reflex  arc  through  the  lower  end  of  the  cord. 

2.  Gluteal  reflex,  consisting  of  contraction  of  the  glutei  muscles  when  the 
skin  over  the  buttock  is  stimulated  ;  it  takes  place  through  the  segments 
giving  origin  to  the  fourth  and  fifth  lumbar  nerves. 

3.  Cremasteric  reflex,  consisting  of  a  contraction  of  the  cremaster  muscle 
and  a  retraction  of  the  testicle  toward  the  abdominal  ring  when  the  skin 
on  the  inner  side  of  the  thigh  is  stimulated  ;  it  depends  upon  the  integ- 
rity of  the  segments  giving  origin  to  the  first  and  second  lumbar  nerves. 

4.  Abdominal  reflex,  consisting  of  a  contraction  of  the  abdominal  muscles 
when  the  skin  upon  the  side  of  the  abdomen  is  gently  scratched  ;  its 
production  requires  the  integrity  of  the  spinal  segments  from  the  eighth 
to  the  twelfth. 

5.  Epigastric  reflex,  consisting  of  a  slight  muscular  contraction  in  the 
neighborhood  of  the  epigastrium  when  the  skin  between  the  fourth  and 
sixth  ribs  is  stimulated  ;  it  requires  the  integrity  of  the  cord  between  the 
fourth  and  seventh  dorsal  nerves. 

6.  The  scapular  reflex  consists  of  a  contraction  of  the  scapular  muscles 
when  the  skin  between  the  scapulae  is  stimulated  ;    it  depends  upon  the 
integrity  of  the  cord  between  the  fifth  cervical  and  third  dorsal  nerves. 
The  superficial  reflexes,  though  variable,  are  generally  present  in  health. 

They  are  increased  or  exaggerated  when  the  gray  matter  of  the  cord  is 
abnormally  excited,  as  in  tetanus,  strychnin-poisoning,  and  disease  of  the 
lateral  columns,  leading  to  arrest  of  their  normal  functions.  The  tendon 
or  deep  reflexes  are  also  of  great  value  in  diagnosing  the  condition  of  the 
spinal  segments.  They  are  induced  by  a  sharp  blow  upon  a  tendon.  The 
following  are  the  principal  forms  : 

1.  Patellar  reflex,  or  knee-jerk,  consisting  of  a  contraction  of  the  extensor 
muscles  of  the  thigh  when  the  ligamentum  patella  is  struck  between  the 
patella  and  tibia.  This  reflex  is  best  observed  when  the  legs  are 
freely  hanging  over  the  edge  of  a  table.  The  patellar  reflex  is  generally 
present  in  health,  being  absent  in  only  two  per  cent.;  it  is  greatly  exag- 
gerated in  lateral  sclerosis  and  in  descending  degeneration  of  the  cord  ; 
it  is  absent  in  locomotor  ataxia  and  in  atrophic  lesions  of  the  anterior 
gray  corn u x. 

2.  Ankle-jerk  or  Reflex.  —  If  the  extensor  muscles  of  the  leg  be  placed 


SPINAL   CORD.  181 

upon  the  stretch  and  the  tendo  Achillis  be  sharply  struck,  a  quick  exten- 
sion of  the  foot  will  take  place. 
3.  Ankle-clonus.  —  This  consists  of  a  series  of  rhythmic  reflex  contractions 
of  the  gastrocnemius  muscle,  varying  in  frequency  from  six  to  ten  a 
second.  To  elicit  this  reflex,  pressure  is  made  upon  the  sole  so  as  sud- 
denly and  energetically  to  flex  the  foot  at  the  ankle,  thus  putting  the 
tendo  Achillis  upon  the  stretch.  The  rhythmic  movements  thus  pro- 
duced continue  as  long  as  the  tension  is  maintained.  Ankle-clonus  is 
never  present  in  health,  but  is  very  marked  in  lateral  sclerosis  of  the 
cord. 

The  toe  reflex,  peroneal  reflex ',  and  zvrist  reflex  are  also  present  in  scle- 
rosis of  the  lateral  columns  and  in  the  late  rigidity  of  hemiplegia. 

Special  Nerve  Centers  in  Spinal  Cord.  —  Throughout  the  spinal 
cord  there  are  a  number  of  special  nerve  centers,  capable  of  being  excited 
reflexly  and  of  producing  complex  coordinated  movements.  Though  for 
the  most  part  independent  in  action,  they  are  subject  to  the  controlling 
influences  of  the  medulla  and  brain. 

1.  Ciliospinal  center,  situated  in  the  cord  between  the  lower  cervical  and 
the  third  dorsal  vertebra.  It  is  connected  with  the  dilatation  of  the 
pupil  through  fibers  which  emerge  in  this  region  and  enter  the  cervical 
sympathetic.  Stimulation  of  the  cord  in  this  locality  causes  dilatation 
of  the  pupil  on  the  same  side  ;  destruction  of  the  cord  is  followed  by 
contraction  of  the  pupil. 

2.  Genitospinal  center,  situated  in  the  lower  part  of  the  cord.  This  is  a 
complex  center,  and  comprises  a  series  of  subordinate  centers  for  the 
control  of  the  muscular  movements  involved  in  the  acts  of  defecation, 
micturition,  and  ejaculation  of  semen,  and  of  the  movements  of  the 
uterus  during  parturition,  etc. 

3.  Vaso-?nolor  centers,  giving  origin  to  both  vaso-constrictor  and  vaso- 
dilator fibers,  which  are  distributed  throughout  the  cord.  Though  acting 
reflexly,  they  are  under  the  dominating  influence  of  the  center  in  the 
medulla. 

4.  Sweat-centers  are  also  present  in  various  parts  of  the  cord. 

2.  As  a  Conductor. 

The  lateral  columns,  particularly  the  posterior  portions,  the  "pyramidal 
tracts,"  and  the  columns  of  Tiirck,  are  the  channels  through  which  pass 
the  voluntary  motor  impulses  from  the  brain  to  the  large  multipolar  nerve- 
cells,  in  the  anterior  cornua  of  gray  matter,  and  through  them  become 


182  HUMAN    PHYSIOLOGY. 

connected  with  the  anterior  roots  which  transmit  the  motor  stimuli  to  the 
muscles. 

The  anterior  columns,  especially  the  portion  surrounding  the  anterior 
cornua,  the  "  anterior  radicular  zones,"  are  composed  of  short,  longitudi- 
nal commissural  fibers,  which  serve  to  connect  different  segments  of  the 
spinal  cord,  a  condition  required  for  the  coordination  of  muscular  move- 
ments. 

The  posterior  columns  are  composed  of  short  and  long  commissural 
fibers  which  connect  different  segments  of  the  cord.  They  are  insensible 
to  direct  irritation,  but  aid  in  the  coordination  of  muscular  movements  in 
walking,  standing,  running,  etc.  Degeneration  of  the  posterior  columns 
gives  rise  to  the  lack  of  muscular  coordination  observed  in  locomotor 
ataxia. 

The  gray  matter,  and  especially  that  portion  immediately  surrounding  the 
central  canal,  transmits  the  sensory  nerve-fibers  from  the  posterior  roots  up 
to  the  brain.  Decussation  of  the  sensory  fibers  takes  place  throughout  the 
whole  length  of  the  gray  matter. 

The  multipolar  cells  of  the  anterior  cornua  are  connected  with  the 
generation  and  transmission  of  motor  impulses  outward ;  are  centers  for 
reflex  movements ;  are  the  trophic  centers  for  the  motor  nerves  and 
muscle-fibers  to  which  they  are  distributed.  The  anterior  roots  give  pas- 
sage to  the  vaso-constrictor  and  vaso-dilator  fibers,  which  exert  an  influ- 
ence upon  the  caliber  of  the  blood-vessels.  Complete  destruction  of  the 
anterior  horns  is  followed  by  paralysis  of  motion,  degeneration  of  the  an- 
terior roots,  atrophy  of  muscles  and  bones,  and  abolition  of  reflex  move- 
ments. 

Paralysis  from  Injuries  of  the  Spinal  Cord. 

Seat  of  Lesion. — If  it  be  in  the  lower  part  of  the  sacral  canal,  there  is 
paralysis  of  the  compressor  urethra;,  accelerator  urinse,  and  sphincter  ani 
muscles  ;  no  paralysis  of  the  muscles  of  the  leg. 

At  the  Upper  Limit  of  the  Sacral  Region. — Paralysis  of  the  muscles  of 
the  bladder,  rectum,  and  anus  ;  loss  of  sensation  and  motion  in  the  muscles 
of  the  legs,  except  those  supplied  by  the  anterior  crural  and  obturator — 
viz.,  psoas  iliacus,  Sartorius,  pectineus,  adductores  longus,  magnus,  and 
brevis,  obturator,  vasti  externus  and  internus,  etc. 

At  the  Upper  Limit  of \the  Lumbar  Region. — Sensation  and  motion 
paralyzed  in  both  legs  ;  loss  of  power  over  the  rectum  and  bladder ;  paraly- 
sis of  the  muscular  walls  of  the  abdomen,  interfering  with  expiratory 
movements. 


CRANIAL   NERVES.  183 

At  the  Lower  Portion  of  the  Cervical  Region. — Paralysis  of  the  legs, 
etc.,  as  in  the  foregoing  ;  in  addition,  paralysis  of  all  the  intercostal  muscles 
and  consequent  interference  with  respiratory  movements  ;  paralysis  of  mus- 
cles of  the  upper  extremities,  except  those  of  the  shoulders. 

Above  the  Middle  of  the  Cervical  Region. — In  addition  to  the  preceding, 
difficulty  of  deglutition  and  vocalization,  contraction  of  the  pupils,  paraly- 
sis of  the  diaphragm,  scalene  muscles,  intercostals,  and  many  of  the  acces- 
sory respiratory  muscles  ;  death  resulting  immediately  from  arrest  of  res- 
piratory movements. 


CRANIAL    NERVES. 

The  cranial  nerves  come  off  from  the  base  of  the  brain,  pass  through 
the  foramina  in  the  walls  of  the  cranium,  and  are  distributed  to  the  skin, 
muscles,  and  organs  of  sense  in  the  face  and  head. 

According  to  the  classification  of  Soemmering,  there  are  twelve  pairs  of 
nerves,  enumerating  them  from  before  backward,  as  follows — viz. : 

First  pair,  or  olfactory.  Seventh  pair,  or  facial   (portio  dura). 

Second  pair,  or  optic.  Eighth  pair,  or  auditory  (  portio  mol- 
Third  pair,  or  motor  oculi  communis.       lis) . 

Fourth    pair,    or   patheticus    (  tro-  Ninth  pair,  or  glosso-pharyngeal. 

chlearis).  Tenth  pair,  or  pneumogastric. 

Fifth  pair,  or  trifacial  (trigeminus).  Eleventh  pair,  or  spinal  accessory. 

Sixth  pair,  or  abducens.  Twelfth  pair,  or  hypoglossal. 

The  cranial  nerves  may  also  be  classified  physiologically,  according  to 
their  function,  into  three  groups  : 

1 .  Nerves  of  special  sense. 

2.  Nerves  of  motion. 

3.  Nerves  of  general  sensibility. 

First  Pair.  Olfactory. 
Apparent  Origin. — From  the  inferior  and  internal  portion  of  the  ante- 
rior lobes  of  the  cerebrum  by  three  roots — viz.,  an  external  white  root, 
which  passes  across  the  fissure  of  Sylvius  to  the  middle  lobe  of  the  cere- 
brum ;  an  internal  white  root,  from  the  most  posterior  part  of  the  anterior 
lobe  ;  a. gray  root,  from  the  gray  matter  in  the  posterior  and  inner  portion 
of  the  inferior  surface  of  the  anterior  lobe. 

Deep  Origin, — Not  satisfactorily  determined. 


184  HUMAN   PHYSIOLOGY. 

Distribution. — The  olfactory  nerve,  formed  by  the  union  of  the  three 
roots,  passes  forward  along  the  under  surface  of  the  anterior  lobe  to  the 
ethmoid  bone,  where  it  expands  into  the  olfactory  bulb.  This  bulb  con- 
tains ganglionic  cells  and  is  grayish  in  color  and  soft  in  consistency  ;  it  gives 
off  from  its  under  surface  from  fifteen  to  twenty  nerve  filaments,  the  true 
olfactory  nerves,  which  pass  through  the  cribriform  plate  of  the  ethmoid 
bone  and  are  distributed  to  the  Schneiderian  mucous  membrane.  This 
membrane  extends  from  the  cribriform  plate  of  the  ethmoid  bone  down- 
ward, about  one  inch. 

Properties. — The  olfactory  nerves  give  rise  to  neither  motor  nor  sensory 
phenomena  when  stimulated.  They  carry  simply  the  special  impressions 
of  odorous  substances.  Destruction  or  injury  of  the  olfactory  bulbs  is 
attended  by  a  loss  of  the  sense  of  smell. 

Function. — Governs  the  sense  of  smell.  Conducts  the  impressions 
which  give  rise  to  odorous  sensations. 

Second  Pair.     Optic. 

Apparent  Origin. — From  the  anterior  portion  of  the  optic  commissure. 

Deep  Origin. — The  origins  and  connections  of  the  optic  tract  are  very 
complex.  The  immediate  origins  are  bands  of  fibers  from  the  thalamus 
opticus  and  anterior  corpora  quadrigemina.  The  corpora  geniculata  are 
interposed  ganglia.     The  ultimate  roots  are  traced — 

1.  By  a  broad  band  of  fibers — "  the  optic  radiation  of  Gratiolet  " — to  the 
psycho-optic  centers  in  the  occipital  lobes. 

2.  To  the  gyrus  hippocampi  and  sphenoid  lobes. 

3.  Through  the  corpus  callosum  to  the  motor  areas  of  the  opposite  cerebral 
hemispheres. 

4.  To  the  frontal  region  by  "  Meynert's  commissure." 

5.  To  the  spinal  cord. 

6.  To  the  corpora  geniculata,  pulvinar,  and  anterior  corpula  geniculata  by 
ganglionic  roots. 

Distribution. — The  two  roots  unite  to  form  a  flattened  band,  the  optic 
tract,  which  winds  around  the  crus  cerebri  to  decussate  with  the  nerve  of 
the  opposite  side,  forming  the  optic  chiasm.  The  decussation  of  fibers  is 
not  complete  ;  some  of  the  fibers  of  the  left  optic  tract  going  to  the  outer 
half  of  the  eye  of  the  same  side  and  to  the  inner  half  of  (he  eye^  of  the 
opposite  side ;  the  same  holds  true  for  the  right  optic  tract. 


CRANIAL    NERVES.  185 

The  optic  nerves  proper  arise  from  the  commissure,  pass  forward  through 
the  optic  foramina,  and  are  finally  distributed  in  the  retina. 

Properties. — They  are  insensible  to  ordinary  impressions,  and  convey 
only  the  special  impressions  of  light.  Division  of  one  of  the  nerves  is 
attended  by  complete  blindness  in  the  eye  of  the  corresponding  side.  ' 

Hemiopia  and  Hemianopsia. — Owing  to  the  decussation  of  the  fibers 
in  the  optic  chiasm,  division  of  the  optic  tract  produces  loss  of  sight  in  the 
outer  half  oi  the  eye  of  the  same  side,  and  in  the  inner  half  'of  the  eye  of 
the  opposite  side,  the  blind  part  being  separated  from  the  normal  part  by  a 
vertical  line.  The  term  hemiopia  is  applied  to  the  loss  of  function  or 
paralysis  of  the  one  half  of  the  retina  ;  hemianopsia  is  applied  to  the 
blindness  in  the  field  of  vision.  If,  for  example,  the  right  optic  tract  be 
divided,  there  will  be  hemiopia  in  the  outer  half  of  the  right  eye  and  inner 
half  of  the  left  eye,  thus  causing  left  lateral  hemianopsia,  and  as  the  two 
halves  are  affected  which  correspond  in  normal  vision,  the  condition  is 
known  as  homonymous  hemianopsia.  Lesion  of  the  anterior  part  of  the 
optic  chiasm  causes  blindness  in  the  inner  half  of  the  two  eyes. 

Functions. — Governs  the  sense  of  sight.  Receives  and  conveys  to  the 
brain  the  luminous  impressions  which  give  rise  to  the  sensation  of  sight. 

The  reflex  movements  of  the  iris  are  called  forth  by  the  optic  nerve. 
When  an  excess  of  light  falls  upon  the  retina,  the  impression  is  carried 
back  to  the  tubercula  quadrigemina,  where  it  is  transformed  into  a  motor 
impulse,  which  then  passes  outward  through  the  motor  oculi  nerve  to  the 
contractile  fibers  of  the  iris  and  diminishes  the  size  of  the  pupil.  The 
absence  of  light  is  followed  by  a  dilatation  of  the  pupil. 

Third  Pair.     Motor  Oculi  Communis. 

Apparent  Origin. — From  the  inner  surface  of  the  crura  cerebri. 

Deep  Origin. — By  three  sets  of  filaments  coming  from  the  oculomo- 
torius  nucleus,  which  lies  under  the  aqueduct  of  Sylvius  ;  these  three 
groups  of  filaments  are  destined  for  the  innervation  of  the  muscles  of  the 
eyeball,  the  sphincter  pupillse,  and  the  ciliary  muscle.  By  filaments  com- 
ing from  the  lenticular  nucleus,  corpora  quadrigemina,  optic  thalamus  ; 
these  filaments  converge  to  form  a  main  trunk,  which  winds  around  the 
eras  cerebri,  in  front  of  the  pons  Varolii. 

Distribution. — The  nerve  then  passes  forward,  and  enters  the  orbit 
through  the  sphenoid  fissure,  where  it  divides  into  a  superior  branch  dis- 

l3 


186  HUMAN   PHYSIOLOGY. 

tributed  to  the  superior  rectus  and  levator  palpebrce  muscles  ;  an  inferior 
branch,  sending  branches  to  the  internal  and  inferior  recti  and  the  inferior 
oblique  muscles  ;  filaments  also  pass  into  the  ciliary  or  ophthalmic  ganglion  ; 
from  this  ganglion  the  ciliary  nerves  arise,  which  enter  the  eyeball  and  are 
distributed  to  the  circular  fibers  of  the  iris  and  the  ciliary  muscle.  The 
third  nerve  also  receives  filaments  from  the  cavernous  plexus  of  the  sym- 
pathetic and  from  the  fifth  nerve. 

Properties. — Irritation  of  the  root  of  the  nerve  produces  contraction  of 
the  pupil,  internal  strabismus,  and  muscular  movements  of  the  eye,  but  no 
pain.  Division  of  the  nerve  is  followed  by  ptosis  (falling  of  the  upper  eye- 
lid) ;  external  strabismus,  due  to  the  unopposed  action  of  the  external 
rectus  muscle ;  paralysis  of  the  accommodation  of  the  eye ;  dilatation  of  the 
pupil  from  paralysis  of  the  circular  fibers  of  the  iris  and  ciliary  muscle  ;  and 
inability  to  rotate  the  eye,  slight  protrusion,  and  double  vision.  The  images 
are  crossed ;  that  of  the  paralyzed  eye  is  a  little  above  that  of  the  sound, 
and  its  upper  end  inclined  toward  it. 

Function. — Governs  movements  of  the  eyeball  by  animating  all  the 
muscles  except  the  external  rectus  and  superior  oblique,  influences  the 
movements  of  the  iris,  elevates  the  upper  lid,  influences  the  accommodation 
of  the  eye  for  distances.  Can  be  called  into  action  by  ( I )  voluntary  stimuli, 
(2)  by  reflex  action  through  irritation  of  the  optic  nerve. 

Fourth  Pair.     Patheticus. 

Apparent  Origin. — From  the  superior  peduncles  of  the  cerebellum. 

Deep  Origin. — By   fibers   terminating  in   the    corpora  quadrigemina, 

lenticular  nucleus,  valve  of  Vieussens,  and   substance  of  the   cerebellar 

peduncles ;  some  filaments  pass  over  the  median  line  and  decussate  with 
fibers  of  the  opposite  side. 

Distribution. — The  nerve  enters  the  orbital  cavity  through  the  sphenoid 
fissure,  and  is  distributed  to  the  superior  oblique  muscle ;  in  its  course  it 
receives  filaments  from  the  ophthalmic  branch  of  the  fifth  pair  and  the 
sympathetic. 

Properties. — When  the  nerve  is  irritated,  muscular  movements  are  pro- 
duced in  the  superior  oblique  muscle,  and  the  pupil  of  the  eye  is  turned 
downzvard  and  outward.  Division  or  paralysis  lessens  the  movements  and 
rotation  of  the  globe  downward  and  outward.  The  diplopia  consequent 
upon  this  paralysis  is  homonymous,  one  image  appearing  above  the  other. 


CRANIAL   NERVES.  187 

The  image  of  the  paralyzed  eye  is  below,  its  upper  end  inclined  toward 
that  of  the  sound  eye. 

Function. — Governs  the  movements  of  the  eyeball  produced  by  the 
action  of  the  superior  oblique  muscles. 

Sixth  Pair.*     Abducens.     Motor  Oculi  Externus. 
Apparent  Origin. — From  the  groove  between  the  anterior  pyramidal 
body  and  the  pons  Varolii,  where  it  arises  by  two  roots. 

Deep  Origin. — From  the  gray  matter  of  the  medulla  oblongata. 

Distribution. — The  nerve  then  passes  into  the  orbit  through  the  sphe- 
noid fissure,  and  is  distributed  to  the  external  rectus  muscle.  Receives 
filaments  from  the  cervical  portion  of  the  sympathetic,  through  the  carotid 
plexus,  and  spheno -palatine  ganglion. 

Properties. — When  irritated,  the  external  rectus  muscle  is  thrown  into 
convulsive  movements  and  the  eyeball  is  turned  outward.  When  divided 
ox  paralyzed,  this  muscle  is  paralyzed,  motion  of  the  eyeball  outward  past 
the  median  line  is  impossible,  and  the  homonymous  diplopia  increases  as 
the  object  is  moved  outward  past  this  line.  The  images  are  upon  the  same 
plane  and  parallel.  Internal  strabismus  results  because  of  the  unopposed 
action  of  the  internal  rectus. 

Function. — To  turn  the  eyeball  outward. 

Fifth  Pair.     Trifacial.     Trigeminal. 
Apparent  Origin. — By  two  roots  from  the  side  of  the  pons  Varolii. 

Deep  Origin. — The  deep  origin  of  the  two  roots  is  the  upper  part  of 
the  floor  and  anterior  wall  of  the  fourth  ventricle,  by  three  bundles  of  Ali- 
ments, one  of  which  anastomoses  with  the  auditory  nerve  ;  another  passes 
to  the  lateral  tract  of  the  medulla  ;  while  a  third,  grayish  in  color,  goes  to 
the  restiform  bodies,  and  may  be  traced  to  the  point  of  the  calamus  scrip- 
torius. 

Filaments  of  origin  have  been  traced  to  the  "  trigeminal  sensory  nu- 
cleus," located  on  a  level  with  the  point  of  exit  of  the  nerve,  and  to  the 
posterior  gray  horns  of  the  cord,  as  low  down  as  the  middle  of  the  neck. 

*The  sixth  nerve  is  considered  in  connection  with  the  third  and  fourth  nerves,  since 
they  together  constitute  the  motor  apparatus  by  which  the  ocular  muscles  are  excited  to 
action. 


188  HUMAN    PHYSIOLOGY. 

Distribution. — The  large  root  of  the  nerve  passes  obliquely  upward  and 
forward  to  the  ganglion  of  Gasser,  which  receives  filaments  of  communi- 
cation from  the  carotid  plexus  of  the  sympathetic.  It  then  divides  into 
three  branches  : 

1.  Ophthalmic  branch,  which  receives  communicating  filaments  from  the 
sympathetic,  and  sends  sensitive  fibers  to  all  the  motor  nerves  of  the 
eyeball.  It  is  distributed  to  the  ciliary  ganglion,  to  the  lacrymal  gland, 
sac,  and  caruncle,  to  the  conjunctiva,  integument  of  the  upper  eyelid, 
forehead,  side  of  head  and  nose,  anterior  portion  of  the  scalp,  ciliary 
muscle,  and  iris. 

2.  Superior  maxillary  branch,  sends  branches  to  the  sphenopalatine 
ganglion,  integument  of  the  temple  and  lower  eyelid,  side  of  the  forehead 
nose,  cheek,  upper  lip,  teeth  of  the  upper  jaw,  and  alveolar  processes. 

3.  Inferior  maxillary  branch,  which,  after  receiving  in  its  course  filaments 
from  the  small  root  and  from  the  facial,  is  distributed  to  the  submaxil- 
lary ganglion,  the  parotid  and  sublingual  glands,  external  auditory 
meatus,  mucous  membrane  of  the  mouth,  anterior  two  thirds  of  the 
tongue  (lingual  branch),  gums,  arches  of  the  palate,  teeth  of  the  lower 
jaw,  and  integument  of  the  lower  part  of  the  face,  and  to  the  muscles  of 
mastication. 

The  small  root  passes  forward  beneath  the  ganglion  of  Gasser,  through 
the  foramen  ovale,  and  joins  the  inferior  maxillary  division  of  the  large 
root,  which  then  divides  into  an  anterior  and  a  posterior  branch,  the  former 
of  which  is  distributed  to  the  muscles  of  mastication — viz.,  temporal,  mas- 
seter,  and  internal  and  external  pterygoid  muscles. 

Properties. — It  is  the  most  acutely  sensitive  nerve  in  the  body,  and 
endows  all  the  parts  to  which  it  is  distributed  with  general  sensibility. 

Irritation  of  the  large  root,  or  of  any  of  its  branches,  will  give  rise  to 
marked  evidence  of  pain  ;  the  various  forms  of  neuralgia  of  the  head  and 
face  being  occasioned  by  compression,  disease,  or  exposure  of  some  of  its 
terminal  branches. 

Division  of  the  large  root  within  the  cranium  is  followed  at  once  by  a 
complete  abolition  of  all  sensibility  in  the  head  and  face,  but  is  not  attended 
by  any  loss  of  motion.  The  integument,  the  mucous  membranes,  and  the 
eye  may  be  lacerated,  cut,  or  bruised,  without  the  animal  exhibiting  any 
evidence  of  pain.  At  the  same  time  the  lacrymal  secretion  is  diminished, 
the  pupil  becomes  contracted,  the  eyeball  is  protruded,  and  the  sensibility 
of  the  tongue  is  abolished. 

The  reflex  movements  of  deglutition  are  also  somewhat  impaired,  the 


CRANIAL    NERVES.  189 

impression  of  the  food  being  unable  to  reach  and  excite  the  nerve  center 
in  the  medulla  oblongata. 

Galvanization  of  the  small  root  produces  movements  of  the  muscles  of 
mastication  ;  section  of  the  root  causes  paralysis  of  these  muscles,  and  the 
jaw  is  drawn  to  the  opposite  side  by  the  action  of  the  opposing  muscles. 

Influences  of  the  Special  Senses. — After  division  of  the  large  root 
within  the  cranium,  a  disturbance  in  the  nutrition  of  the  special  senses 
sooner  or  later  manifests  itself. 

Sight. — In  the  course  of  twenty-four  hours  the  eye  becomes  very  vascular 
and  inflamed,  the  cornea  becomes  opaque  and  ulcerates,  the  humors  are 
discharged,  and  the  eye  is  totally  destroyed. 

Smell. — The  nasal  mucous  membrane  swells  up,  becomes  fungous,  and 
is  liable  to  bleed  on  the  slightest  irritation.  The  mucous  is  increased  in 
amount,  so  as  to  obstruct  the  nasal  passages ;  the  sense  of  smell  is  finally 
abolished. 

Hearing. — At  times  the  hearing  is  impaired  from  disorders  of  nutrition 
in  the  middle  ear  and  external  auditory  meatus. 

Alteration  in  the  nutrition  of  the  special  senses  is  not  marked  if  the  sec- 
tion is  made  posterior  to  the  ganglion  of  Gasser  and  to  the  anastomos- 
ing filaments  of  the  sympathetic,  which  join  the  nerves  at  this  point ; 
but  if  the  ganglion  be  divided,  these  effects  are  very  noticeable,  owing 
to  the  section  of  the  sympathetic  filaments. 

Function. — Gives  sensibility  to  all  parts  of  the  head  and  face  to  which 
it  is  distributed ;  through  the  small  root,  endows  the  masticatory  muscles 
with  motion  ;  through  fibers  from  the  sympathetic,  governs  the  nutrition  of 
the  special  senses. 

Seventh  Pair.     Portio  Dura.     Facial  Nerve. 

Apparent  Origin. — From  the  groove  between  the  olivary  and  restiform 
bodies  at  the  lateral  portion  of  the  medulla  oblongata  and  below  the  margin 
of  the  pons  Varolii. 

Deep  Origin. — From  a  nucleus  of  large  cells  in  the  floor  of  the  fourth 
ventricle,  below  the  nucleus  of  origin  of  the  sixth  pair,  with  which  it  is 
connected.  Some  filaments  are  traceable  to  the  lenticular  nucleus  of  the 
opposite  side.  Some  of  the  fibers  cross  the  median  line  and  decussate.  It 
is  intimately  associated  with  the  nerve  of  Wrisberg  at  its  origin. 

Distribution. — From  its  origin  the  facial  nerve  passes  into  the  internal 
auditory  meatus,  and  then,  in  company  with  the  nerve  of  Wrisberg,  enters 


190  HUMAN    PHYSIOLOGY. 

the  aqueduct  of  Fallopius.  The  filaments  of  the  nerve  of  Wrisberg  are 
supplied  with  a  ganglion,  of  a  reddish  color,  having  nerve-cells.  These 
filaments  unite  with  those  of  the  root  of  the  facial  to  form  a  common  trunk, 
which  emerges  at  the  stylomastoid  foramen. 

In  the  aqueduct  the  facial  gives  off  the  following  branches — viz.  : 

1.  Large  petrosal  nerve,  which  passes  forward  to  the  spheno-palatine,  or 
Meckel's  ganglion,  and  through  this  to  the  levator  palati  and  azygos 
uvulae  muscles,  which  receive  motor  influence  from  this  source. 

2.  Small  petrosal  nerve,  passing  to  the  otic  ganglion  and  thence  to  the 
tensor  tympani  muscle,  endowing  it  with  motion. 

3.  Ty?npanic  branch,  giving  motion  to  the  stapedius  muscle. 

4.  Chorda  tympani  nerve,  which,  after  entering  the  posterior  part  of  the 
tympanic  cavity,  passes  forward  between  the  malleus  and  incus,  through 
the  Glaserian  fissure,  and  joins  the  lingual  branch  of  the  fifth  nerve. 
It  is  then  distributed  to  the  mucous  membrane  of  the  anterior  two  thirds 
of  the  tongue  and  the  submaxillary  glands. 

After  emerging  from  the  stylomastoid  foramen,  the  facial  nerve  sends 
branches  to  the  muscles  of  the  ear,  the  occipitofrontalis,  the  digastric,  the 
palatoglossi,  and  palatopharyngei ;  after  which  it  passes  through  the  paro- 
tid gland  and  divides  into  the  temporofacial  and  cervicofacial  branches, 
which  are  distributed  to  the  superficial  muscles  of  the  face— viz.,  occi- 
pitofrontalis, corrugator  supercilii,  orbicularis  palpebrarum,  levator  labii 
superioris  et  alseque  nasi,  buccinator,  levator  anguli  oris,  orbicularis  oris, 
zygomatici,  depressor  anguli  oris,  platysma  myoides,  etc. 

Properties. — Undoubtedly  a  motor  nerve  at  its  origin,  but  in  its  course 
receives  sensitive  filaments  from  the  fifth  pair  and  the  pneumogastric. 

Irritation  of  the  nerve,  after  its  emergence  from  the  stylomastoid  fora- 
men, produces  convulsive  movements  in  all  the  superficial  muscles  of  the 
face.  Division  of  the  nerve  at  this  point  causes  paralysis  of  these  muscles 
on  the  side  of  the  section,  constituting  facial  paralysis,  the  phenomena 
of  which  are  a  relaxed  and  immobile  condition  of  the  same  side  of  the 
face  ;  the  eyelids  remain  open,  from  paralysis  of  the  orbicularis  palpe- 
brarum ;  the  act  of  winking  is  abolished  ;  the  angle  of  the  mouth  droops, 
and  saliva  constantly  drains  away ;  the  face  is  drawn  over  to  the  second 
side  ;  the  face  becomes  distorted  upon  talking  or  laughing  ;  mastication 
is  interfered  with,  the  food  accumulating  between  the  gums  and  cheek, 
from  paralysis  of  the  buccinator  muscle  ;  fluids  escape  from  the  mouth  in 
drinking  ;  articulation  is  impaired,  the  labial  sounds  being  imperfectly 
pronounced. 


CRANIAL   NERVES.  191 

Properties  of  the  Branches  givin  off  in  the  Aqueduct  oj  Fullupius. — 'lhe 
large  petrosal,  when  irritated,  throws  the  levator  palati  and  azygos  uvulae 
muscles  into  contraction.  Paralysis  of  this  nerve,  from  deep-seated  lesions, 
produces  a  deviation  of  the  uvula  to  the  sound  side,  a  drooping  of  the 
palate,  and  an  inability  to  elevate  it. 

The  small  petrosal  influences  hearing  by  animating  the  tensor  tympani 
muscles ;  when  paralyzed,  there  occurs  partial  deafness  and  an  increased 
sensibility  to  sonorous  impressions. 

The  tympanitic  branch  animates  the  stapedius  muscle  and  influences 
audition. 

The  chorda  tympani  influences  the  circulation  and  the  secretion  of 
saliva  in  the  submaxillary  glands,  and  governs  the  sense  of  taste  in  the 
anterior  two  thirds  of  the  tongue.  Galvanization  of  the  chorda  tympani 
dilates  the  blood-vessels,  increases  the  quantity  and  rapidity  of  the  stream 
of  blood,  and  increases  the  secretion  of  saliva.  Division  of  the  nerve  is 
followed  by  contraction  of  the  vessels,  an  arrest  of  the  secretion,  and  a 
diminution  of  the  sense  of  taste  on  the  same  side. 

Function. — The  facial  is  the  nerve  of  expression,  and  coordinates  the 
muscles  employed  to  delineate  the  various  emotions,  influences  the  sense 
of  taste,  deglutition,  movements  of  the  uvula  and  soft  palate,  the  tension  of 
the  membrana  tympani,  and  the  secretions  of  the  submaxillary  and  parotid 
glands.     Indirectly  influences  smell,  hearing,  and  vision. 

Eighth  Pair.     Portio  Mollis.     Auditory  Nerve. 

Apparent  Origin. — From  the  upper  and  lateral  portion  of  the  medulla 
oblongata,  just  below  the  margin  of  the  pons  Variolii. 

Deep  Origin. — By  two  roots  from  the  floor  of  the  fourth  ventricle,  each 
root  consisting  of  a  number  of  gray  filaments,  some  of  which  decussate  in 
the  median  line  ;  the  external  root  has  a  gangliform  enlargement  containing 
fusiform  nerve-cells. 

Distribution. — The  two  roots  wind  around  the  restiform  bodies  and 
enter  the  internal  auditory  meatus,  and  divide  into  an  anterior  branch,  dis- 
tributed to  the  cochlea,  and  a  posterior  branch,  distributed  to  the  vestibule 
and  semicircular  canals. 

Properties. — They  are  soft  in  consistence,  grayish  in  color,  consisting 
of  axis-cylinders  with  a  medullary  sheath  only  ;  they  are  not  sensible  to 
ordinary  impressions,  but  convey  the  impression  of  sound. 


192  HUMAN   PHYSIOLOGY. 

Function. — Governs  the  sense  of  hearing.  Receives  and  conducts  to 
the  brain  the  impression  of  sound,  which  gives  rise  to  the  sensations  of 
hearing. 

Ninth  Pair.     Glossopharyngeal. 

Apparent  Origin. — Partly  from  the  medulla  oblongata  and  the  inferior 
peduncles  of  the  cerebellum. 

Deep  Origin. — From  the  lower  portion  of  the  gray  substance  in  the 
floor  of  the  fourth  venticle. 

This  nerve  has  two  ganglia  :  The  jugular  ganglion  includes  only  a  por- 
tion of  the  root-filaments  ;  the  ganglion  of  Andersch  includes  all  the 
fibers  of  the  trunk. 

Distribution. — The  trunk  of  the  nerve  passes  downward  and  forward, 
receiving  near  the  ganglion  of  Andersch  fibers  from  the  facial  and  pneu- 
mogastric  nerves.  It  divides  into  two  large  branches,  one  of  which  is 
distributed  to  the  base  of  the  tongue,  the  other  to  the  pharynx.  In  its 
course  it  sends  filaments  to  the  otic  ganglion  ;  a  tympanic  branch  which 
gives  sensibility  to  the  mucous  membrane  of  the  fenestra  rotunda,  fenestra 
ovalis,  and  Eustachian  tube  ;  lingual  branches  to  the  base  of  the  tongue  ; 
palatal  branches  to  the  soft  palate,  uvula,  and  tonsils  ;  pharyngeal  branches 
to  the  mucous  membrane  of  the  pharynx. 

Properties. — Irritation  of  the  roots  at  their  origin  calls  forth  evidences 
of  pain ;  it  is,  therefore,  a  sensory  nerve,  but  its  sensibility  is  not  so  acute 
as  that  of  the  trifacial.  Irritation  of  the  trunk  after  its  exist  from  the 
cranium  produces  contraction  of  the  muscles  of  the  palate  and  pharynx, 
owing  to  the  presence  of  anastomosing  motor  fibers. 

Division  of  the  nerve  abolishes  sensibility  in  the  structures  to  which  it  is 
distributed  and  impairs  the  sense  of  taste  in  the  posterior  third  of  the 
tongue  (see  Sense  of  Taste). 

Function. — Governs  sensibility  of  pharynx,  presides  partly  over  the 
sense  of  taste,  and  controls  reflex  movements  of  deglutition  and  vomiting. 

Tenth  Pair.     Pneumogastric.     Par  Vagum. 

Apparent  Origin. — From  the  lateral  side  of  the  medulla  oblongata, 
just  behind  the  olivary  body. 

Deep  Origin. — In  the  gray  nuclei  in  the  lower  half  of  the  floor  of  the 
fourth  ventricle  and  in  the  substance  of  the  restiform  body.  Some  fila- 
ments are  traced  along  the  restiform   tract,  toward  the  cerebellum,  and 


CRANIAL   NERVES.  193 

others  to  the  median  line  of  the  floor  of  the  fourth  ventricle,  where  many 
of  them  decussate. 

This  nerve  has  two  ganglia  :  one  in  the  jugular  foramen,  called  the 
ganglion  of  the  root,  and  another  outside  of  the  cranial  cavity  on  the 
trunk,  the  ganglion  of  the  trunk. 

Distribution. — The  filaments  from  the  roots  unite  to  form  a  single  trunk, 
which  leaves  the  cavity  of  the  cranium,  through  the  jugular  foramen,  in 
company  with  the  spinal  accessory  and  glossopharyngeal.  It  soon  receives 
an  anastomotic  branch  from  the  spinal  accessory,  and  afterward  branches 
from  the  facial,  the  hypoglossal,  and  the  anterior  branches  of  the  two  upper 
cervical  nerves. 

As  the  nerve  passes  down  the  neck  it  sends  off  the  following  main 
branches  : 

1.  Pharyngeal  newes,  which  assist  in  forming  the  pharyngeal  plexus, 
which  is  distributed  to  the  mucous  membrane  and  to  the  muscles  of  the 
pharynx. 

2.  Superior  laryngeal  nerve,  which  enters  the  larynx  through  the  thyro- 
hyoid membrane,  and  is  distributed  to  the  mucous  membrane  lining  the 
interior  of  the  larynx,  and  to  the  cricothyroid  muscle  and  the  inferior 
constrictor  of  the  pharynx.  The  "  depressor  nerve"  found  in  the  rabbit, 
is  formed  by  the  union  of  two  branches,  one  from  the  superior  laryngeal, 
the  other  from  the  main  trunk  ;  it  passes  downward  to  be  distributed  to 
the  heart. 

3.  Inferior  laryngeal,  which  sends  its  ultimate  branches  to  all  the  intrinsic 
muscles  of  the  larynx  except  the  cricothyroid,  and  to  the  inferior  con- 
strictor of  the  pharynx. 

4.  Cardiac  branches  given  off  from  the  nerve  throughout  its  course,  which 
unite  with  the  sympathetic  fibers  to  form  the  cardiac  plexus,  to  be  dis- 
tributed to  the  heart. 

5.  Pulmonary  branches,  which  form  a  plexus  of  nerves,  and  are  distributed 
to  the  bronchi  and  their  ultimate  terminations,  the  lobules  and  air-cells. 
From  the  right  pneumogastric  nerve  branches  are  distributed  to  the  mu- 
cous membrane  and  muscular  coats  of  the  stomach  and  intestines,  and  to 
the  liver,  spleen,  kidneys,  and  suprarenal  capsules. 

Properties. — At  its  origin  the  pneumogastric  nerve  is  sensory,  as  shown 
by  direct  irritation  or  galvanization,  though  its  sensibility  is  not  very  marked. 
In  its  course  it  exhibits  motor  properties,  from  anastomosis  with  motor 
nerves. 

The  pharyngeal  branches  assist   in   giving   sensibility  to   the   mucous 


194  HUMAN    PHYSIOLOGY. 

membrane  of  the  pharynx,  and  influence  reflex  phenomena  of  deglutition 
through  motor  fibers  which  they  contain,  derived  from  the  spinal  accessory. 

The  superior  laryngeal  nerve  endows  the  upper  portion  of  the  larynx 
with  sensibility  ;  protects  it  from  the  entrance  of  foreign  bodies  ;  by  con- 
ducting impressions  to  the  medulla,  excites  the  reflex  movements  of  deglu- 
tition and  respiration  ;  through  the  motor  filaments  it  contains,  produces 
contraction  of  the  cricothyroid  muscle. 

Division  of  the  ' '  depressor  nerve ' '  and  galvanization  of  the  central 
end  retard  and  even  arrest  the  pulsations  of  the  heart,  and  by  depressing 
the  vaso-motor  center,  diminish  the  pressure  of  blood  in  the  large  vessels, 
by  causing  dilatation  of  the  intestinal  vessels  through  the  splanchnic 
nerves. 

The  inferior  laryngeal  contains,  for  the  most  part,  motor  fibers  from 
the  spinal  accessory.  When  irritated,  produces  movement  in  the  laryngeal 
muscles.  When  divided,  is  followed  by  paralysis  of  these  muscles,  except 
the  cricothyroid,  impairment  of  phonation,  and  an  embarrassment  of  the 
respiratory  movements  of  the  larynx,  and,  finally,  death  from  suffocation. 

The  cardiac  branches,  through  filaments  derived  from  the  spinal  acces- 
sory, exert  a  direct  inhibitory  action  upon  the  heart.  Division  of  the 
pneumogastrics  in  the  neck  increases  the  frequency  of  the  heart's  action. 
Galvanization  of  the  peripheral  ends  diminishes  the  heart's  pulsations,  and, 
if  sufficiently  powerful,  paralyzes  it  in  diastole. 

The  pulmonary  branches  give  sensibility  to  the  bronchial  mucous 
membrane  and  govern  the  movements  of  respiration.  Division  of  both 
pneumogastrics  in  the  neck  diminishes  the  frequency  of  the  respiratory 
movements,  which  may  fall  as  low  as  four  to  six  a  minute  ;  death  usually 
occurs  in  from  five  to  eight  days.  Feeble  galvanization  of  the  central  ends 
of  the  divided  nerves  accelerates  respiration  ;  powerful  galvanization 
retards,  and  may  even  arrest,  the  respiratory  movements. 

The  gastric  branches  give  sensibility  to  the  mucous  coat,  and  through 
sympathetic  filaments,  which  join  the  pneumogastrics  high  up  in  the  neck, 
give  motion  to  the  muscular  coat  of  the  stomach.  They  influence  the 
secretion  of  gastric  juice,  aid  the  process  of  digestion  and  absorption  from 
the  stomach. 

The  hepatic  branches,  probably  through  anastomosing  sympathetic  fila- 
ments, influence  the  secretion  of  bile  and  the  glycogenic  function  of  the 
liver ;  division  of  the  pneumogastrics  in  the  neck  produces  congestion  of 
the  liver,  diminishes  the  density  of  the  bile,  and  arrests  the  glycogenic 
function ;  galvanization  of  the  central  ends  exaggerates  the  glycogenic 
function  and  makes  the  animal  diabetic. 


CRANIAL   NERVES.  195 

The  intestinal  branches  give  sensibility  and  motion  to  the  small  intestines, 
and  when  divided,  purgative  generally  fail  to  produce  evacuation. 

Function. — A  great  sensitive  nerve,  which,  through  anastomotic  fila- 
ments from  motor  sources,  influences  deglutition,  the  action  of  the  heart, 
the  circulatory  and  respiratory  systems,  voice,  the  secretions  of  the  stomach, 
intestines,  and  various  glandular  organs. 


Eleventh  Pair.     Spinal  Accessory. 

Apparent  Origin. — By  two  sets  of  filaments  : 

1 .  A  bulbar  or  medullary  set,  four  or  five  in  number,  from  the  lateral  or 
motor  tract  of  the  lower  half  of  the  medulla  oblongata,  below  the  origin 
of  the  pneumogastric. 

2.  A  spinal  set,  from  six  to  eight  in  number,  from  the  lateral  portion  of  the 
spinal  cord,  between  the  anterior  and  posterior  roots  of  the  upper  four 
or  five  cervical  nerves. 

Deep  Origin. — The  medullary  portion  arises  in  a  nucleus  in  the  lower 
half  of  the  floor  of  the  fourth  ventricle,  common  to  the  pneumogastric  and 
glossopharyngeal  nerves.  The  spinal  portion  has  its  origin  in  an  elongated 
nucleus  lying  along  the  external  surface  of  the  anterior  cornua  of  the  spinal 
cord,  extending  down  to  the  fifth  cervical  vertebra. 

Distribution. — From  this  origin  the  fibers  unite  to  form  a  main  trunk, 
which  enters  the  cranial  cavity  through  the  foramen  magnum,  where  it  is 
at  times  joined  by  fibers  from  the  posterior  roots  of  the  two  upper  cervical 
nerves,  and  sends  filaments  to  the  ganglion  of  the  root  of  the  pneumo- 
gastric. After  emerging  from  the  cranial  cavity  through  the  jugular  for- 
amen, it  sends  a  branch  to  the  pneumogastric  and  receives  others  in  return, 
and  also  from  the  second,  third,  and  fourth  cervical  nerves.  It  divides 
into  two  branches  : 

1.  An  internal  or  anastomotic  branch,  made  up  of  filaments  coming  prin- 
cipally from  the  medulla  oblongata  ;  it  is  distributed  to  the  muscles  of 
the  pharynx  through  the  pharyngeal  nerves  coming  from  the  pneumo- 
gastric ;  to  all  the  muscles  of  the  larynx,  except  the  cricothyroid,  through 
the  inferior  laryngeal  nerve  ;  to  the  heart,  by  filaments  which  reach  it 
through  the  pneumogastric  nerve. 

2.  An  external  branch,  which  is  distributed  to  the  sterno-cleido-mastoid 
and  trapezius  muscles  ;  these  muscles  also  receive  filaments  from  the 
cervical  nerves. 


196  HUMAN   PHYSIOLOGY. 

Properties. — At  its  origin  it  is  5  purely  motor  nerve,  but  in  its  course  it 
exhibits  some  sensibility,  which  it  received  from  anastomosing  fibers. 

Destruction  of  the  medullary  root,  by  tearing  it  from  its  attachment  by 
means  of  forceps,  impairs  the  action  of  the  muscles  of  deglutition  and 
destroys  the  power  of  producing  vocal  sounds  by  paralysis  of  the  laryngeal 
muscles,  without,  however,  interfering  with  the  respiratory  movements  of 
the  larynx,  these  being  controlled  by  other  motor  nerves.  The  normal 
rate  of  movement  of  the  heart  is  also  impaired  by  destruction  of  the  medul- 
lary root. 

Irritation  of  the  external  branch  throws  the  trapezius  and  sternomastoid 
muscles  into  convulsive  movements,  though  section  of  the  nerve  does  not 
produce  complete  paralysis,  as  they  are  also  supplied  with  motor  influence 
from  the  cervical  nerves.  The  sternomastoid  and  trapezius  muscles  per- 
form movements  antagonistic  to  those  of  respiration,  fixing  the  head,  neck, 
and  upper  part  of  the  thorax,  and  delaying  the  expiratory  movement  during 
the  acts  of  pushing,  pulling,  straining,  etc. ,  and  in  the  production  of  a  pro- 
longed vocal  sound,  as  in  singing.  When  the  external  branch  alone  is 
divided,  in  animals,  they  experience  shortness  in  breath  during  exercise, 
from  a  want  of  coordination  of  the  muscles  of  the  limbs  and  respiration  ; 
and  while  they  can  make  a  vocal  sound,  it  can  not  be  prolonged. 

Function. — Governs  phonation  by  its  influence  upon  the  vocal  move- 
ments of  the  glottis  ;  influences  the  movements  of  deglutition,  inhibits  the 
action  of  the  heart,  and  controls  certain  respiratory  movements  associated 
with  sustained  or  prolonged  muscular  efforts  and  phonation. 

Twelfth  Pair.     Hypoglossal  or  Sublingual. 

Apparent  Origin. — By  two  groups  of  filaments  from  the  medulla  ob- 
longata, in  the  grooves  between  the  olivary  body  and  the  anterior  pyramid. 

Deep  Origin. — From  the  hypoglossal  nucleus,  situated  deep  in  the 
substance  of  the  medulla,  on  a  level  with  the  lowest  portion  of  the  floor  of 
the  fourth  ventricle  ;  some  decussating  filaments  have  been  traced  to  a 
higher  encephalic  center. 

Distribution. — The  trunk  formed  by  a  union  of  the  root  filament  passes 
out  of  the  cranial  cavity  through  the  anterior  condyloid  foramen,  occa- 
sionally receiving  a  filament  from  the  lateral  and  posterior  portion  of  the 
medulla  oblongata.  After  emerging  from  the  cranium,  it  sends  filaments 
to  the  sympathetic  and  pneumogastric  ;  it  anastomoses  with  the  lingual 
branch  of  the  fifth  pair,  and  receives  and  sends  filaments  to  the  upper  cer- 


MEDULLA   OBLONGATA.  197 

vical  nerves.  The  nerve  is  finally  distributed  to  the  sternohyoid,  sterno- 
thyroid, omohyoid,  thyrohyoid,  styloglossi,  hyoglossi,  geniohyoid,  genio- 
hyoglossi,  and  the  intrinsic  muscles  of  the  tongue. 

Properties. — A  purely  motor  nerve  at  its  origin,  but  derives  sensibility 
outside  the  cranial  cavity  from  anastomosis  with  the  cervical,  pneumogas- 
tric,  and  fifth  nerves. 

Irritation  of  the  nerve  gives  rise  to  convulsive  movements  of  the  tongue 
and  slight  evidences  of  sensibility. 

Division  of  the  nerve  abolishes  all  movements  of  the  tongue  and  inter- 
feres considerably  with  the  act  of  deglutition. 

When  the  hypoglossal  nerve  is  involved  in  hemiplegia,  the  tip  of  the 
tongue  is  directed  to  the  paralyzed  side  when  the  tongue  is  protruded, 
owing  to  the  unopposed  action  of  the  geniohyoglossus  on  the  sound  side. 

Articulation  is  considerably  impaired  in  paralysis  of  this  nerve,  great 
difficulty  being  experienced  in  the  pronunciation  of  the  consonantal  sounds. 

Mastication  is  performed  with  difficulty,  from  inability  to  retain  the  food 
between  the  teeth  until  it  is  completely  triturated. 

Function. — Governs  all  the  movements  of  the  tongue  and  influences 
the  functions  of  mastication,  deglutition,  and  articulaton. 


MEDULLA  OBLONGATA. 

The  medulla  oblongata  is  the  expanded  portion  of  the  upper  part  of 
the  spinal  cord.  It  is  pyramidal  in  form  and  measures  1*4  inches  in  length, 
^  of  an  inch  in  breadth,  y^  of  an  inch  in  thickness,  and  is  divided  into  two 
lateral  halves  by  the  anterior  and  posterior  median  fissures,  which  are  con- 
tinuous with  those  of  the  cord.  Each  half  is  again  subdivided  by  minor 
grooves  into  four  columns — viz;,  anterior  pyramid,  lateral  and  tract  olivary 
body,  resliform  body,  and  posterior  pyramid. 

1.  The  anterior  pyramid  is  composed  partly  of  fibers  continuous  with  those 
of  the  anterior  column  of  the  spinal  cord,  but  mainly  of  fibers  derived 
from  the  lateral  tract  of  the  opposite  side  by  decussation.  The  united 
fibers  then  pass  upward  through  the  pons  Varolii  and  crura  cerebri,  and 
for  the  most  part  terminate  in  the  corpus  striatum  and  cerebrum. 

2.  The  lateral  tract  is  continuous  with  the  lateral  columns  of  the  cord  ;  its 
fibers  in  passing  upward  take  three  directions — viz.,  an  external  bundle 
joins  the  restiform  body,  and  passes   into  the  cerebellum ;  an  internal 


198 


HUMAN   PHYSIOLOGY. 


bundle  decussates  at  the  median  line  and  joins  the  opposite  anterior  pyra- 
mid ;  a  middle  bundle  ascends  beneath  the  olivary  body,  behind  the 
pons,  to  the  cerebrum,  as  the  fasciculus  teres.  The  olivary  body  of  each 
side  is  an  oval  mass,  situated  between  the  anterior  pyramid  and  restiform 
body ;  it  is  composed  of  white  matter  externally  and  gray  matter  inter- 
nally, forming  the  corpus  dentatum. 


Fig.  23. — View  of  Cerebellum   in  Section,  and  of   Fourth  Ventricle,  with 
the  Neighboring  Parts. — {From  Sappey.) 

1.  Median  groove  fourth  ventricle,  ending  below  in  the  calamus  scriptorius ,  with  the 
longitudinal  eminences  formed  by  the  fasciculi  teretes,  one  on  each  side.  2.  The 
same  groove,  at  the  place  where  the  white  streaks  of  the  auditory  nerve  emerge  from 
it  to  cross  the  floor  of  the  ventricle.  3.  Inferior  peduncle  of  the  cerebellum,  formed 
by  the  restiform  body.  4.  Posterior  pyramid ;  above  this  is  the  calamus  scriptorius. 
5,  5.  Superior  peduncle  of  cerebellum,  or  processus  e  cerebello  ad  testes.  6.  6. 
Fillet  to  the  side  of  the  crura  cerebri.  7,  7.  Lateral  grooves  of  the  crura  cerebri. 
8.   Corpora  quadrigemina.     {After  Hirschfeld  and  Leveille.') 


3.  The  restiform  body,  continuous  with  the  posterior  column  of  the  cord, 
also  receives  fibers  from  the  lateral  column.  As  the  restiform  bodies 
pass  upward  they  diverge  and  form  a  space  (the  fourth  ventricle),  the 
floor  of  which  is  formed  by  gray  matter,  and  then  turn  backward  and 
enter  the  cerebellum. 

4.  The  posterior  pyramid  is  a  narrow  white  cord  bordering  the  posterior 
median  fissure  ;  it  is  continued  upward,  in  connection  with  the  fasciculus 
teres,  to  the  cerebrum. 


MEDULLA    OBLONGATA.  199 

The  gray  matter  of  the  medulla  is  continuous  with  that  of  the  cord. 
It  is  arranged  with  much  less  regularity,  becoming  blended  with  the  white 
matter  of  the  different  columns,  with  the  exception  of  the  anterior.  By  the 
separation  of  the  posterior  columns  the  transverse  commissure  is  exposed, 
forming  part  of  the  floor  of  the  fourth  ventricle  ;  special  collections  of  gray 
matter  are  found  in  the  posterior  portions  of  the  medulla,  connected  with 
the  roots  of  origin  of  different  cranial  nerves. 

Properties  and  Functions. — The  medulla  is  excitable  anteriorly  and 
sensitive  posteriorly  to  direct  irritation.     It  serves — 

1.  As  a  conductor  of  sensitive  impressions  upward  from  the  cord,  through 
the  gray  matter  to  the  cerebrum. 

2.  As  a  conductor  of  voluntary  impulses  from  the  brain  to  the  spinal  cord 
and  nerves,  through  its  anterior  pyramids. 

3.  As  a  conductor  of  coordinating  impulses  from  the  cerebellum,  through 
the  restiform  bodies  to  the  spinal  cord. 

As  an  Independent  Reflex  Center. — The  medulla  oblongata  contains 
special  collections  of  gray  matter,  constituting  independent  nerve  centers 
presiding  over  different  functions,  some  of  which  are  as  follows — viz. : 

1 .  A  center  which  controls  the  movements  of  mastication,  through  afferent 
and  efferent  nerves.      (See  p.  96. ) 

2.  A  center  reflecting  impressions  which  influence  the  secretion  of  saliva. 
(See  p.  99.) 

3.  A  center  for  sucking,  mastication,  and  deglutition,  whence  are  derived 
motor  stimuli  exciting  to  action  and  coordinating  the  muscles  of  the 
palate,  pharynx,  and  esophagus,  necessary  for  the  swallowing  of  the 
food. 

The  secretion  of  saliva  is  also  controlled  by  a  center  in  the  medulla. 

NERVOUS   CIRCLE   OF   DEGLUTITION. 
Second  and  Third  Stages. 
Palatal  branch  of  the  fifth  pair. 
Pharyngeal  branches  of  the  glossopharyngeal. 
Superior  laryngeal  branches  of  the  pneumogastric. 
Esophageal  branches  of  the  pneumogastric. 

Pharyngeal  branches  of  the  pneumogastric,  derived  from 

the  spinal  accessory. 
Hypoglossal  and  branches  of  the  cervical  plexus. 
Inferior  or  recurrent  laryngeal. 

Motor  filaments  of  the  third  division  of  the  fifth  pair. 
Portio  dura. 


Excitor 

or 

centripetal 

nerves. 

Motor 

or 

centrifugal 

nerves. 


200  HUMAN    PHYSIOLOGY. 

4.  A  center  which  coordinates  the  muscles  concerned  in  the  act  of  vomit- 
ing. 

5.  A  speech  center,  coordinating  the  various  muscles  necessary  for  the  ac- 
complishment of  articulation  through  the  hypoglossal,  facial  nerves,  and 
the  second  division  of  the  fifth  pair. 

6.  A  center  for  the  harmonization  of  muscles  concerned  in  expression,  re- 
flecting its  impulses  through  the  facial  nerve. 

7.  A  cardiac  center,  which  exerts  (i)  an  accelerating  influence  over  the 
heart's  pulsations  through  accelerating  nerve-fibers  emerging  from  the 
cervical  portion  of  the  cord,  entering  the  inferior  cervical  ganglion,  and 
thence  passing  to  the  heart;  (2)  an  inhibitory  ox  retarding  influence 
upon  the  action  of  the  heart,  through  fibers  of  the  spinal  accessory  nerve 
running  in  the  trunk  of  the  pneumogastric.  The  cardio-inhibitory  center 
is  in  a  state  of  tonic  excitement  and  continuously  sends  impulses  to  the 
heart  which  exert  an  inhibitory  influence  upon  its  action.  It  may  be 
stimulated  directly  by  anemia  as  well  as  by  venous  hyperemia  of  the 
blood-vessels  of  the  medulla  and  increased  venosity  of  the  blood.  It  is 
excited  reflexly  by  the  stimulation  of  the  central  end  of  the  vagus,  sciatic, 
and  splanchnic  nerves. 

8.  A  vaso-motor  center,  which,  by  alternately  contracting  and  dilating  the 
blood-vessels  through  nerves  distributed  in  their  walls,  regulates  the 
quantity  of  blood  distributed  to  an  organ  or  tissue,  and  thus  influences 
nutrition,  secretion,  and  calorification.  The  vaso-motor  center  is  situated 
in  the  medulla  oblongata  and  pons  Varolii,  between  the  corpora  quadri- 
gemina  and  the  calamus  scriptorius.  The  vaso-motor  fibers  having  their 
origin  in  this  center  descend  through  the  interior  of  the  cord,  emerge 
through  the  anterior  roots  of  spinal  nerves,  enter  the  ganglia  of  the  sym- 
pathetic, and  thence  pass  to  the  walls  of  the  blood-vessels,  and  maintain 
an  arterial  tonus;  they  may  be  divided  into  two  classes — viz.,  vaso- 
dilators (<?.  g.,  chorda  tympani)  and  vaso-constrictors  {e.g.,  sympathetic 
fibers). 

Division  of  the  cord  at  the  lower  border  of  the  medulla  is  followed  by  a 
dilatation  of  the  entire  vascular  system  and  a  marked  fall  of  the  blood  pres- 
sure. Galvanic  stimulation  of  the  divided  surface  of  the  cord  is  followed 
by  a  contraction  of  the  blood-vessels  and  a  rise  in  the  blood  pressure. 

The  vaso-motor  center  is  stimulated  directly  by  the  condition  of  the 
blood  in  the  medulla  oblongata.  When  the  blood  is  highly  venous  this 
center  becomes  very  active,  the  blood-vessels  throughout  the  body  are  con- 
tracted, and  the  blood  current  becomes  swifter ;  sudden  anemia  of  the 
medulla  has  a  similar  effect.     The  action  of  the  vaso-motor  center  may  be 


IONS    VAROLII.  201 

accelerated,  with  attendent  rise  of  blood  pressure,  by  irritation  of  certain 
afferent  nerve-fibers.  These  are  known  as  pressor  fibers.  On  the  other 
hand,  its  action  may  be  depressed  by  other  fibers,  with  attendant  fall  of 
blood  pressure.     These  are  known  as  depressor  fibers. 

9.  A  diabetic  center,  irritation  of  which  causes  an  increase  in  the  amount 
of  urine  secreted  and  the  appearance  of  a  considerable  quantity  of  sugar 
in  the  urine. 

10.  Respiratory  center,  situated  near  the  origin  of  the  pneumogastric 
nerves,  presides  over  the  movements  of  respiration  and  its  modifications, 
laughing,  singing,  sobbing,  sneezing,  etc.  It  may  be  excited  rcjlexly  by 
the  presence  of  carbonic  acid  in  the  lungs  irritating  the  terminal  pneu- 
mogastric filaments  ;  or  automatically,  according  to  the  character  of  the 
blood  circulating  through  it ;  an  excess  of  carbonic  acid  or  a  diminution 
of  oxygen  increasing  the  number  of  respiratory  movements  ;  a  reverse 
condition  diminishing  the  respiratory  movements. 

11.  A  spasm  center,  stimulation  of  which  gives  rise  to  convulsive  phe- 
nomena, such  as  coughing,  sneezing,  etc. 

12.  A  center  for  certain  ocular  functions,  governing  the^  closure  of  the  eye- 
lids and  dilatation  of  the  pupil. 

13.  A  sweat  center  is  also  localized  in  the  medulla. 

NERVOUS   CIRCLE   OF   RESPIRATION. 

Entirely  Reflex. 

P     •  r  Pulmonary  branches  of  the  pneumogastric. 

I  Superior  laryngeal. 
.  •        ,      J  Trifacial,  or  fifth  pair. 

_  I  Nerves  of  general  sensibility. 

I  Sympathetic  nerve. 

yt  r  Phrenic,  distributed  to  the  diaphragm. 

Intercostals,  distributed  to  the  intercostal  muscles. 
■  r      1      -!  Facial  nerve,  or  portio  dura,  to  the  facial  muscles. 

External  branch  of  spinal  accessory,  to  the  trapezius  and 
I      sterno-cleido-mastoid  muscles. 


nerves. 


PONS  VAROLII. 

The  pons  Varolii  unites  the  cerebrum  above,  the  cerebellum  behind, 
and  the  medulla  oblongata  below.     It  consists  of  transverse  and   longi- 
tudinal fibers,  amidst  which  are  irregularly  scattered  collections  of  gray  or 
vesicular  nervous  matter. 
14 


202  HUMAN    PHYSIOLOGY. 

The  transverse  fibers  unite  the  two  lateral  halves  of  the  cerebellum. 
The  longitudinal  fibers  are  continuous — 

1.  With  the  anterior  pyramids  of  the  medulla  oblongata,  which,  interlacing 
with  the  deep  layers  of  the  transverse  fibers,  ascend  to  the  crura  cerebri, 
forming  their  superficial  or  fasciculated  portions. 

2.  With  fibers  derived  from  the  olivary  fasciculus,  some  of  which  pass  to 
the  tubercula  quadrigemina,  while  others,  uniting  with  fibers  from  the 
lateral  and  posterior  columns  of  the  medulla,  ascend  in  the  deep  or 
posterior  portions  of  the  crura  cerebri. 

Properties  and  Functions. — The  superficial  portion  is  insensible  and 
inexcitable  to  direct  irritation  ;  the  deeper  portion  appears  to  be  excitable, 
consisting  of  descending  motor  fibers  ;  the  posterior  portions  are  sensible, 
but  inexcitable  to  irritation. 

Transmits  motor  impulses  and  sensory  impressions  from  and  to  the 
cerebrum. 

The  gray  ganglionic  matter  consists  of  centers  which  convert  impressions 
into  conscious  sensations  and  originate  motor  impulses,  these  taking  place 
independent  of  any  intellectual  process  ;  they  are  the  seat  of  instinctive 
reflex  acts,  the  centers  which  assist  in  the  coordination  of  the  automatic 
movements  of  station  and  progression. 


CRURA    CEREBRI. 

The  crura  cerebri  are  largely  composed  of  the  longitudinal  fibers  of  the 
pons  (anterior  pyramids,  fasciculi  teretes) ;  after  emerging  from  the  pons 
they  increase  in  size,  and  become  separated  into  two  portions  by  a  layer 
of  dark-gray  matter,  the  locus  niger. 

The  superfii  ial  portion,  the  crusta,  composed  of  the  anterior  pyramids, 
constitutes  the  motor  tract,  which  terminates,  for  the  most  part,  in  the  cor- 
pus striatum,  but  to  some  extent,  also,  in  the  cerebrum ;  the  deep  portion, 
made  up  of  the  fasciculi  teretes  and  posterior  pyramids  and  accessory  fibers 
from  the  cerebellum,  constitutes  the  sensory  tract  (the  tegmentum),  which 
terminates  in  the  optic  thalamus  and  cerebrum. 

Function. — The  crura  are  conductors  of  motor  impulses  and  sensory 
impressions  ;  the  gray  matter,  the  locus  niger,  assists  in  the  coordination  of 


CORPORA   QUADRIGEMINA.  203 

the  complicated  movements  of  the  eyeball  and  iris,  through  the  motor  oculi 
communis  nerve.  They  also  assist  in  the  harmonization  of  general  mus- 
cular movements,  section  of  one  crus  giving  rise  to  peculiar  movements  of 
rotation  and  somersaults  forward  and  backward. 


CORPORA    QUADRIGEMINA. 

The  corpora  quadrigemina  are  four  small,  rounded  eminences,  two 
on  *each  side  of  the  median  line,  situated  immediately  behind  the  third 
ventricle,  and  beneath  the  posterior  border  of  the  corpus  callosum. 

The  anterior  tubercles  are  oblong  from  before  backward,  and  larger  than 
the  posterior,  which  are  hemispheric  in  shape  ;  they  are  grayish  in  color, 
but  consist  of  white  matter  externally  and  gray  matter  internally. 

Both  the  anterior  and  posterior  tubercles  are  connected  with  the  optic 
thalami  by  commissural  bands,  named  the  anterior  and  posterior  brachia, 
respectively.  They  receive  fibers  from  the  olivary  fasciculus  and  fibers 
from  the  cerebellum,  which  press  upward  to  enter  the  optic  thalami. 

The  corpora  geniculata  are  situated,  one  on  the  inner  side  and  one  on 
the  outer  side  of  each  optic  tract,  behind  and  beneath  the  optic  thalamus, 
and  from  their  position  are  named  the  corpora  geniculate  interna  and  ex- 
terna ;  they  give  origin  to  fibers  of  the  optic  nerve. 

Functions. — The  corpora  quadrigemina  are  centers  associated  with  the 
visual  centers.  Destruction  of  these  tubercles  is  immediately  followed  by 
a  loss  of  the  sense  of  sight ;  moreover,  their  action  in  vision  is  crossed, 
owing  to  the  decussation  of  the  optic  tracts,  so  that  if  the  tubercle  of  the 
right  side  be  destroyed  by  disease  or  extirpated,  in  a  pigeon,  the  sight  is 
lost  in  the  eye  of  the  opposite  side,  and  the  iris  loses  its  mobility. 

The  tubercula  quadrigemina  as  nerve  centers  preside  over  the  reflex 
movements  which  cause  a  dilatation  or  contraction  of  the  iris,  irritation  of 
the  tubercles  causing  contraction,  destruction  causing  dilatation.  Removal 
of  the  tubercles  on  one  side  produces  a  temporary  loss  of  power  of  the 
opposite  side  of  the  body,  and  a  tendency  to  move  around  an  axis  is  mani- 
fested, as  after  a  section  of  one  crus  cerebri,  which,  however,  may  be  due 
to  giddiness  and  loss  of  sight. 

They  also  assist  in  the  coordination  of  the  complex  movements  of  the 
eye,  and  regulate  the  changes  of  the  iris  during  the  movements  of  accom- 
modation for  distance. 


204  HtfMAN    PHYSIOLOGY. 

CORPORA  STRIATA  AND   OPTIC  THALAMI. 

The  corpora  striata  are  two  large  ovoid  collections  of  gray  matter, 
situated  at  the  base  of  the  cerebrum,  the  larger  portions  of  which  are 
embedded  in  the  white  matter,  the  smaller  portions  projecting  into  the 
anterior  part  of  the  lateral  ventricle.  Each  striated  body  is  divided,  by  a 
narrow  band  of  white  matter,  into  two  portions — viz.  : 

1.  The  caudate  nucleus,  the  intraventricular  portion,  which  is  conic  in 
shape,  having  its  apex  directed  backward,  as  a  narrow,  tail-like  process. 

2.  The  lenticular  nucleus,  embedded  in  the  white  matter,  and  for  the  most 
part  external  to  the  ventricle.  On  the  outer  side  of  the  lenticular  nucleus 
is  found  a  narrow  band  of  white  matter,  the  external  capsule ;  and 
between  it  and  the  convolutions  of  the  island  of  Reil,  a  thin  band  of  gray 
matter,  the  claustrum. 

The  corpora  striata  are  grayish  in  color,  and  when  divided,  present  trans- 
verse striations,  from  the  intermingling  of  white  fibers  and  gray  cells. 

The  optic  thalami  are  two  oblong  masses  situated  in  the  ventricles 
posterior  to  the  corpora  striata,  and  resting  upon  the  posterior  portion  of  the 
crura  cerebri.  The  internal  surface,  projecting  into  the  lateral  ventricles,  is 
white,  but  the  interior  is  grayish,  from  a  commingling  of  both  white  fibers 
and  gray  cells.  Separating  the  lenticular  nucleus  from  the  caudate  nucleus 
and  the  optic  thalamus  is  a  band  of  white  tissue,  the  internal  capsule . 

The  internal  capsule  is  a  narrow,  curved  tract  of  white  matter,  and  is,  for 
the  most  part,  an  expansion  of  the  motor  tract  of  the  crura  cerebri.  It 
consists  of  two  segments — an  anterior,  situated  between  the  caudate  nucleus 
and  the  anterior  surface  of  the  lenticular  nucleus,  and  a  posterior ',  situated 
between  the  optic  thalamus  and  the  posterior  surface  of  the  lenticular 
nucleus.  These  two  segments  unite  at  an  obtuse  angle,  which  is  directed 
toward  the  median  line.  Pathologic  observation  has  shown  that  the  nerve- 
fibers  of  the  direct  and  crossed  pyramidal  tracts  can  be  traced  upward 
through  the  anterior  two  thirds  of  the  posterior  segment  into  the  centrum 
ovale,  where,  for  the  most  part,  they  are  lost ;  a  portion,  however,  remain- 
ing united,  ascend  higher  and  terminate  in  the  paracentral  lobule,  the 
superior  extremity  of  the  ascending  frontal  and  parietal  convolutions. 
Those  of  the  sensory  trad  can  be  traced  upward,  through  the  posterior 
third,  into  the  cerebrum,  where  they  probably  terminate  in  the  hippocam- 
pus major  and  uncinate  convolution. 

Functions. — The  corpora  striata  are  the  centers  in  which  terminate 
some  of  the  fibers  of  the  superficial  or  ?notor  tract  of  the  crura  cerebri ; 


CEREBELLUM.  205 

others  pass  upward  through  the  internal  capsule,  to  be  distributed  to  the 
cerebrum.  It  might  be  inferred,  from  their  anatomic  relations,  that  the  cor- 
pora striata  are  motor  centers.  Irritation  by  a  weak  galvanic  current  pro- 
duces muscular  movements  of  the  opposite  side  of  the  body  ;  destructio?i  of 
their  substance  by  a  hemorrhage,  as  in  apoplexy,  is  followed  by  a  paralysis 
of  motion  of  the  opposite  side  of  the  body,  but  there  is  no  loss  of  sensation. 
When  the  hemorrhagic  destruction  involves  the  fibers  of  the  anterior  two 
thirds  of  the  posterior  segment  of  the  internal  capsule,  and  thus  separates 
them  from  their  trophic  centers  in  the  cortical  motor  region,  a  descending 
degeneration  is  established,  which  involves  the  direct  pyramidal  tract  of 
the  same  side  and  the  crossed  pyramidal  tract  of  the  opposite  side. 

Destruction  of  the  posterior  one  third  of  the  posterior  segment  of  the 
internal  capsule  is  followed  by  a  loss  of  sensation  on  the  opposite  side  of 
the  body  and  a  loss  of  the  senses  of  smell  and  vision  on  the  same  side 
(Charcot).  The  precise  function  of  the  corpora  striata  is  unknown,  but 
they  are  in  some  way  connected  with  motion. 

The  optic  thalami  receives  the  fibers  of  the  tegmentum,  the  posterior 
portion  of  the  crura  cerebri.  They  are  insensible  and  inexcitable  to  direct 
irritation.  Removal  of  one  optic  thalamus,  or  destruction  of  its  substance 
by  disease  or  hemorrhage,  is  followed  by  a  loss  of  sensibility  of  the  oppo- 
site side  of  the  body,  but  there  is  no  loss  of  motion  ;  their  precise  function 
is  also  unknown,  but  they  are  in  some  way  connected  with  sensation.  In 
both  cases  their  action  is  crossed. 


CEREBELLUM. 

The  cerebellum  is  situated  in  the  inferior  fossae  of  the  occipital  bone, 
beneath  the  posterior  lobes  of  the  cerebrum.  It  attains  its  maximum 
weight,  which  is  about  five  ounces,  between  the  twenty-fifth  and  fortieth 
years,  the  proportion  between  the  cerebellum  and  cerebrum  being  as  I  to  8^. 

It  is  composed  of  two  lateral  he?nispheres  and  a  central  elongated  lobe, 
the  verjniform  process  ;  the  two  hemispheres  are  connected  with  each  other 
by  the  fibers  of  the  middle  peduncle,  forming  the  superficial  portion  of  the 
pons  Varolii.  The  cerebellum  is  brought  into  connection  with  the  medulla 
oblongata  and  spinal  cord  through  the  prolongation  of  the  restiform  bodies  ; 
with  the  cerebrum,  by  fibers  passing  upward  beneath  the  corpora  quadri- 
gemina  and  the  optic  thalami,  and  then  forming  part  of  the  diverging 
cerebral  fibers. 


206  HUMAN   PHYSIOLOGY. 

Structure. — It  is  composed  of  both  white  and  gray  matter,  the  former 
being  internal,  the  latter  external,  and  is  convoluted,  for  economy  of  space. 

The  white  matter  consists  of  a  central  stem,  the  interior  of  which  is  a 
dentated  capsule  of  gray  matter,  the  corpus  dentatuni.  From  the  external 
surface  of  the  stem  of  white  matter  processes  are  given  off,  forming  the 
lamina,  which  are  covered  with  gray  matter. 

The  gray  ??iatter  is  convoluted  and  covers  externally  the  laminated  pro- 
cesses ;  a  vertical  section  through  the  gray  matter  reveals  the  following 
<t  uetures  : 

1.  A  delicate  connective-tissue  layer,  just  beneath  the  pia  mater,  containing 
rounded  corpuscles,  and  with  branching  fibers  passing  toward  the  ex- 
ternal surface. 

2.  The  cells  of  Purkinje,  forming  a  layer  of  large,  nucleated,  branched 
nerve-cells  sending  off  processes  to  the  external  layer. 

3.  A  granular  layer  of  small  but  numerous  corpuscles. 

4.  A  nerve-fiber  layer,  formed  by  a  portion  of  the  white  matter. 

Properties  and  Functions. — Irritation  of  the  cerebellum  is  not  fol- 
lowed by  any  evidences  either  of  pain  or  convulsive  movements  ;  it  is, 
therefore,  insensible  and  inexcitable. 

Coordination  of  Movements. — Removal  of  the  superficial  portions  of 
the  cerebellum  in  pigeons  produces  feebleness  and  want  of  harmony  in  the 
muscular  movements ;  as  successive  slices  are  removed,  the  movements 
become  more  irregular,  and  the  pigeon  becomes  restless ;  when  the  last 
portions  are  removed,  all  power  of  flying,  walking,  standing,  etc.,  is  en- 
tirely gone,  and  the  equilibrium  can  not  be  maintained,  the  power  of  coor- 
dinating muscular  movements  being  wholly  lost.  The  same  results  have 
been  obtained  by  operating  on  all  classes  of  animals. 

The  following  symptoms  were  noticed  by  Wagner,  after  removing  the 
whole  or  a  large  part  of  the  cerebellum  : 

1.  A  tendency  on  the  part  of  the  animal  to  throw  itself  on  one  side,  and  to 
extend  the  legs  as  far  as  possible. 

2.  Torsion  of  the  head  on  the  neck. 

3.  Trembling  of  the  muscles  of  the  body,  which  was  general. 

4.  Vomiting  and  occasional  liquid  evacuations. 

Forced  Movements. — Division  of  one  crus  cerebelli  causes  the  animal 
to  fall  on  one  side  and  roll  rapidly  on  its  longitudinal  axis.  According  to 
Schiff,  if  the  peduncle  be  divided  from  behind,  the  animal  falls  on  the  same 
side  as  the  injury  ;  if  the  section  be  made  in  front,  the  animal  turns  to  the 
opposite  side. 


CEREBRUM.  207 

Disease  of  the  cerebellum  partially  corroborates  the  result  of  experi- 
ments ;  in  many  cases  symptoms  of  unsteadiness  of  gait,  from  a  want  of 
coordination,  have  been  noticed. 

Comparative  anatomy  reveals  a  remarkable  correspondence  between  the 
development  of  the  cerebellum  and  the  increase  in  complexity  of  muscular 
actions.  It  attains  a  much  greater  development,  relatively  to  the  rest  of  the 
brain,  in  those  animals  whose  movements  are  very  complex  and  varied  in 
character,  such  as  the  kangaroo,  shark,  and  swallow. 

The  cerebellum  may  possibly  exert  some  influence  over  the  sexual  func- 
tions, but  physiologic  and  pathologic  facts  are  opposed  to  the  idea  of  its 
being  the  seat  of  the  sexual  instinct.  It  appears  to  be  simply  a  center 
for  the  coordination  and  equilibration  of  muscular  movements. 


CEREBRUM. 

The  cerebrum  is  the  largest  portion  of  the  encephalic  mass,  constituting 
about  four  fifths  of  its  weight ;  the  average  weight  of  the  adult  male  brain 
is  from  forty-eight  to  fifty  ounces,  or  about  three  pounds,  while  that  of  the 
adult  female  is  about  five  ounces  less.  After  the  age  of  forty  the  weight 
of  the  cerebrum  gradually  diminishes  at  the  rate  of  one  ounce  every  ten 
years.  In  idiots  the  brain  weight  is  often  below  the  normal,  at  times  not 
amounting  to  more  than  twenty  ounces. 

The  blood-supply  to  the  cerebrum  is  unusually  large,  considering  its 
comparative  bulk,  nearly  one  fifth  of  the  entire  volume  of  blood  in  the  body 
being  distributed  to  it  by  the  carotid  and  vertebral  arteries.  These  vessels 
anastomose  so  freely,  and  are  so  arranged  within  the  cavity  of  the  cranium, 
that  an  obstruction  in  one  vessel  will  not  interfere  with  the  regular  supply  of 
blood  to  the  parts  to  which  its  branches  are  distributed.  A  diminished 
amount,  or  complete  cessation,  of  the  supply  of  blood  is  at  once  followed 
by  a  suspension  of  its  functional  activity. 

The  cerebrum  is  connected  with  the  pons  Varolii  and  medulla  oblongata 
through  the  crura  cerebri,  and  with  the  cerebellum  through  the  superior 
peduncles.  It  is  divided  into  two  lateral  halves,  or  hemispheres,  by  the 
longitudinal  fissure  running  from  before  backward  in  the  median  line  ;  each 
hemisphere  is  composed  of  both  white  and  gray  matter,  the  former  being 
internal,  the  latter  external ;  it  covers  the  surfaces  of  the  hemisphere  which 
are  infolded,  forming  convolutions,  for  economy  of  space. 


208  HUMAN  PHYSIOLOGY. 


Fissures. 


i.  The  fissure  of Sylvius  is  one  of  the  most  important;  it  is  the  first  to 
appear  in  the  development  of  the  fetal  brain,  being  visible  at  about  the 
third  month  ;  in  the  adult  it  is  quite  deep  and  well  marked,  running  from 
the  under  surface  of  the  brain  upward,  outward,  and  backward,  and 
forms  a  boundary  between  the  frontal  and  temporosphenoid  lobes. 

2.  The  fissure  of  Rolando  is  second  in  importance,  and  runs  from  a  point 
on  the  convexity  near  the  median  line  transversely  outward  and  down- 
ward toward  the  fissure  of  Sylvius,  but  does  not  enter  it.  It  separates 
the  frontal  from  the  parietal  lobe. 

3.  The  parietal 'fissure,  arising  a  short  distance  hehind  the  fissure  of  Ro- 
lando, upon  the  convexity  of  the  hemisphere,  runs  downward  and  back- 
ward to  its  posterior  extremity. 

4.  The  parietooccipital  fissure  separates  the  occipital  from  the  parietal 
lobe.  Beginning  upon  the  outer  surface  of  the  cerebrum,  it  is  continued 
on  the  mesial  aspect  downward  and  forward  until  it  terminates  in  the 
calcarine  fissure. 

5.  The  callosomarginal fissure  lies  upon  the  mesial  surface,  where  it  runs 
parallel  with  the  corpus  callosum. 

Secondary  fissures  of  importance  are  found  in  different  lobes  of  the 
cerebrum,  separating  the  various  convolutions.  In  the  anterior  lobe  are 
found  the  precentral,  superior  frontal,  and  inferior  frontal  fissures ;  in 
the  temporosphenoid  lobes  are  found  the  first  and  second  temporo- 
sphenoid fissure ;  in  the  occipital  lobe,  the  calcarine  and  hippocampal 
fissures. 

Convolutions.     Frontal  Lobe. 

The  ascending  frontal  convolution,  situated  in  front  of  the  fissure  of 
Rolando,  runs  downward-  and  forward ;  it  is  continuous  above  with  the 
anterior  frontal,  and  below  with  the  inferior  frontal,  convolution. 

The  superior  frontal  convolution  is  bounded  internally  by  the  longitu- 
dinal fissure,  and  externally  by  the  superior  frontal  fissure  ;  it  is  connected 
with  the  superior  end  of  the  frontal  convolution,  and  runs  downward  and 
forward  to  the  anterior  extremity  of  the  frontal  lobe,  where  it  turns  back- 
ward, and  rests  upon  the  orbital  plate  of  the  frontal  bone. 

The  middle  frontal  convolution,  the  largest  of  the  three,  runs  from  be- 
hind forward,  along  the  sides  of  the  lobe,  to  its  anterior  part ;  it  is 
bounded  above  by  the   superior  and  below  by  the  inferior  frontal  fissures. 

The  inferior  frontal  convolution  winds  around  the  ascending  branch  of 
the  fissure  of  Sylvius,  in  the  anterior  and  inferior  portion  of  the  cerebrum. 


CEREBRUM. 


209 


Parietal  Lobe. — The  ascending  parietal  convolution  is  situated  just 
behind  the  fissure  of  Rolando,  running  downward  and  forward  ;  above,  it 


Fig.  24. — Diagram    showing   Fissures    and    Convolutions    of   the   Left  Side 
of  the  Human  Brain. — (Lanctois'  "Physiology.") 

F.  Frontal.  P.  Parietal.  O.  Occipital.  T.  Temporosphenoid  lobe.  S.  Fissure 
of  Sylvius.  S'.  Hirizontal.  S".  Ascending  ramus  of  S.  c.  Sulcus  centralis,  or 
fissure  of  Rolando.  A.  Ascending  frontal,  and  B.  Ascending  parietal  convolutions. 
Fj.  Superior,  F2.  Middle,  and  F3.  Inferior  frontal  convolutions.  fx.  Superior,  f„. 
Inferior  frontal  fissures.  f3.  Sulcus  prsecentralis.  Px.  Superior  paretial  lobule. 
P2.  Inferior  parietal  lobule,  consisting  of  P9.  Supramarginal  gyrus,  and  P2'.  Angu- 
lar gyrus,  ip.  Sulcus  interpari'  talN.  cm.  Terminat  on  of  callosomarginal  fissure. 
O,.  First,  (32.  Second,  03.  Third  occipital  convolutions,  po.  Parieto-occipi'al 
fissure,  o.  Transverse  occipital  fissure.  o2.  Inferior  longitudinal  occipital  fissure. 
T1.  First,  T2.  Second,  T3.  Temporospheno  d,  convolutions.  tx,  tx.  First,  t2- 
Second,  temporosphenoid  fissures. 


becomes  continuous  with  the  upper  parietal  convolution,  and  below,  winds 
around  to  be  united  with  the  ascending  frontal. 


210  HUMAN   PHYSIOLOGY. 

The  upper  parietal  convolution  is  situated  between  the  parietal  and 
longitudinal  fissures. 

The  supramarginal  convolution  winds  around  the  superior  extremity  of 
the  fissure  of  Sylvius. 

The  angular  convolution,  a  continuation  of  the  preceding,  follows  the 
parietal  fissure  to  its  posterior  extremity,  and  then  makes  a  sharp  angle 
downward  and  forward. 

Temporosphenoid  Lobe. — Contains  three  well-marked  convolutions, 
the  superior,  middle  and  inferior,  separated  by  well-defined  fissures,  and 
continuous  posteriorly  with  the  convolutions  of  the  parietal  lobe. 

The  occipital  lobe  lies  behind  the  parieto-occipital  fissure,  and  contains 
the  superior,  middle  and  inferior  convolutions,  not  well  marked. 

The  central  lobe,  or  island  of  Reil,  situated  at  the  bifurcation  of  the 
fissure  of  Sylvius,  is  a  triangular- shaped  cluster  of  six  convolutions,  the 
gyri  operti,  which  are  connected  with  those  of  the  frontal,  parietal,  and 
temporosphenoid  lobes. 

Upon  the  inner  or  mesial  aspect  of  the  hemisphere  are  found  (Fig.  25) — 

1.  The  paracentral  lobule,  lying  in  the  region  of  the  upper  extremity  of 
the  fissure  of  Rolando  ;  it  contains  the  large  giant  cells  of  Betz.  Injury 
to  this  convolution  is  followed  by  degeneration  of  the  motor  tract. 

2.  The  gyrus  fornicatus,  lying  below  the  callosomarginal  fissure.  Run- 
ning parallel  with  the  corpus  callosum,  it  terminates  at  its  posterior  border 
in  the  hippocampal  gyrus. 

3.  The  gyrus  hippocampus  (H)  is  formed  by  the  union  of  the  preceding 
convolution  with  the  occipitotemporal.  It  runs  forward  and  terminates 
in  a  hooked  extremity — uncus. 

4.  The  quadrate  lobule,  or  precuneus,  lies  between  the  upper  extremity  of 
the  callosomarginal  fissure  and  the  parieto-occipital. 

5.  The  cuneus  lies  posteriorly  to  the  quadrate  lobule.  It  is  a  wedge- 
shaped  mass  inclosed  by  the  calcarine  and  parieto-occipital  fissures. 

Structure. — The  gray  matter  of  the  cerebrum,  about  y$  of  an  inch 
thick,  is  composed  of  five  layers  of  nerve-cells  : 

1.  A  superficial  layer,  containing  a  few  small  multipolar  ganglion  cells. 

2.  Small  ganglion  cells,  pyramidal  in  shape. 

3.  A  layer  of  large  pyramidal  ganglion  cells  with  processes  running  off 
superiorly  and  laterally. 

4.  The  granular  formation  containing  nerve-cells. 

5.  Spindle-shaped  and  branching  nerve-cells  of  a  moderate  size. 


CEREBRUM. 


211 


The  white  matter  consists  of  three  distinct  sets  of  fibers. 
The  diverging  ox  peduncular  fibers  are  mainly  derived  from  the  columns 
of  the  cord  and  medulla  oblongata  ;  passing  upward  through  the  crura 
cerebri,  they  receive  accessory  fibers  from  the  olivary  fasciculus,  corpora 
quadrigemina,  and  cerebellum.     Some  of  the  fibers  terminate  in  the  optic 


Fig.  25. 


-Diagram  showing  Fissures  and  Convolutions  on  Mesial  Aspect  of 
the  Right  Hemisphere. 


Median  aspect  of  the  right  hemisphere.  CC.  Corpus  callosum  divided  longitudinallyi 
Gf.  Gyrus  fornicatus.  H.  Gyrus  hippocampi,  h.  Sulcus  hippocampi.  U.  Unc,- 
nate  gyrus,  cm.  Callosomarginal  fissure.  Fx.  First  frontal  convolution,  c.  Ter- 
minal portion  of  fissure  of  Rolando.  A.  Ascending  frontal,  B.  Ascending  parietal, 
convolution  and  paracentral  lobule.  P/.  Prsecuneus  or  quadrate  lobule.  Oz. 
Cuneus.  Po.  Parieto-occipital  fissure,  o.  Transverse  occipital  fissure,  oc.  Cal- 
carine  fissure,  oc' .  Superior,  oc" .  Inferior,  rami  of  the  same.  D.  Gyrus  descen- 
dens.  T4.  Gyrus  occipitotemporalis  lateralis  (lobulus  fusiformis).  T5.  Gyrus 
occipitotemporalis  medialis  (lobulus  lingualis). 

thalami  and  corpora  striata,  while  others  radiate  into  the  anterior,  mid- 
dle, and  posterior  lobes  of  the  cerebrum. 

2.  The  transverse  commissural  fibers  connect  the  two  hemispheres,  through 
the  corpus  callosum  and  anterior  and  posterior  commissures. 

3.  The  longitudinal  commissural  fibers  connect  different  parts  of  the  same 
hemisphere. 

Functions. — The  cerebral  hemispheres  are  the  centers  of  the  nervous 
system  through  which  are  manifested  all  the  phenomena  of  the  mind  ;  they 


212 


HUMAN   PHYSIOLOGY. 


are  the  centers  in  which  impressions  are  registered  and  reproduced  subse- 
quently as  ideas  ;  they  are  the  seat  of  intelligence,  reason,  and  will. 


Fig.  26. — Side  View  of  the  Brain  of  Man,  with  the  Areas  of  the  Cerebral 
Convolutions  according  to  Ferrier. 

The  figures  are  constructed  by  marking  on  the  brain  of  man,  in  their  respective 
situations ,  the  areas  of  the  brain  of  the  monkey  as  determined  by  experiment,  and 
the  description  of  the  effects  of  stimu'ating  the  various  areas  refers  to  the  brain 
of  the  monkey. 

1.  Advance  of  the  opposite  hind  limb,  as  in  walking.  2,  3,  4.  Complex  movements  of 
the  opposite  leg  and  arm,  and  of  the  trunk,  as  in  swimming,  a,  b,  c,  d.  Individual 
and  combined  movements  of  the  fingers  and  wrists  of  the  opposite  hand.  Prehensile 
movements.  5.  Extension  forward  of  the  opposite  arm  and  hand.  6.  Supination 
and  flexion  of  the  opposite  forearm.  7.  Retraction  and  elevation  of  the  opposite 
angle  of  the  mouth,  by  means  of  the  zygomatic  muscles.  8.  Elevation  of  the  alae 
nasi  and  upper  lip,  with  depression  of  the  lower  lip  on  the  opposite  side.  9,  10. 
Opening  of  the  mouth,  with  (9)  protrusion  and  (10)  retraction  of  the  tongue;  region 
of  aphasia,  bilateral  action.  11.  Retraction  of  the  opposite  angle  of  the  mouth,  the 
head  turned  slightly  to  one  side.  12.  The  eyes  open  widely,  the  pupils  dilate,  and 
the  head  and  eyes  turn  toward  the  opposite  side.  13,  13'.  The  eyes  moved  toward 
the  opposite  side  with  an  upward  (13)  or  downward  (13')  deviation.  The  pupils  are 
generally  contracted.  14.  PricKing  of  the  opposite  ear,  the  head  and  eyes  turn  to 
the  opposite  side,  and  the  pupils  dilate  widely. 


CEREBRUM.  213 

However  important  a  center  the  cerebrum  may  be  for  the  exhibition  of 
this  highest  form  of  nervous  action,  it  is  not  directly  essential  for  the  con- 
tinuance of  life,  for  it  does  not  exert  any  control  over  those  automatic  reflex 
acts,  such  as  respiration,  circulation,  etc.,  which  regulate  the  functions  of 
organic  life. 

From  the  study  of  comparative  anatomy,  pathology,  vivisection,  etc., 
evidence  has  been  obtained  which  throws  some  light  upon  the  physiology 
of  the  cerebral  hemispheres. 

1.  Comparative  anatomy  shows  that  there  is  a  general  connection  between 
the  size  of  the  brain,  its  texture,  the  depth  and  number  of  convolutions, 
and  the  exhibition  of  mental  power.  Throughout  the  entire  animal 
series,  the  increase  in  intelligence  goes  hand  in  hand  with  an  increase  in 
the  development  of  the  brain.  In  man  there  is  an  enormous  increase  in 
size  over  that  of  the  highest  animals,  the  anthropoids.  The  most  culti- 
vated races  of  men  have  the  greatest  cranial  capacity  ;  that  of  the  edu- 
cated European  being  about  Il6  cubic  inches,  that  of  the  Australian 
being  about  60  cubic  inches,  a  difference  of  56  cubic  inches.  Men  dis- 
tinguished for  great  mental  power  usually  have  large  and  well-developed 
brains  ;  that  of  Cuvier  weighed  64  ounces  ;  that  of  Abercrombie,  63 
ounces  ;  the  average  being  about  48  to  50  ounces.  Not  only  the  size,  but, 
above  all,  the  texture,  of  the  brain  must  be  taken  into  consideration. 

2.  Pathology. — Any  severe  injury  or  disease  disorganizing  the  hemispheres 
is  at  once  attended  by  a  disturbance  or  an  entire  suspension  of  mental 
activity.  A  blow  on  the  head,  producing  concussion,  or  undue  pressure 
from  cerebral  hemorrhage,  destroys  consciousness ;  physical  and  chemic 
alterations  in  the  gray  matter  have  been  shown  to  coexist  with  insanity, 
and  with  loss  of  memory,  speech,  etc.  Congenital  defects  of  organization 
from  imperfect  development  are  usually  accompanied  by  a  corresponding 
deficiency  of  intellectual  power  and  of  the  higher  instincts.  Under  these 
circumstances  no  great  advance  in  mental  development  can  be  possible, 
and  the  intelligence  remains  of  a  low  grade.  In  congenital  idiocy  not 
only  is  the  brain  of  small  size,  but  it  is  wanting  in  proper  chemic  com- 
position, phosphorus,  a  characteristic  ingredient  of  the  nervous  tissue, 
being  largely  diminished  in  amount. 

3.  Experimentation  upon  the  lower  animals  by  removing  the  cerebral 
hemispheres  is  attended  by  results  similar  to  those  observed  in  disease 
and  injury.  Removal  of  the  cerebrum  in  pigeons  produces  complete 
abolition  of  intelligence,  and  destroys  the  capability  of  performing  spon- 
taneous movements.  The  pigeon  remains  in  a  condition  of  profound 
stupor,  which  is  not  accompanied,  however,  by  a  loss  of  sensation  or  of 


214  HUMAN   PHYSIOLOGY. 

the  power  of  producing  reflex  or  instinctive  movements.  The  pigeon 
can  be  temporarily  aroused  by  pinching  the  feet,  loud  noises,  lights  placed 
before  the  eyes,  etc.,  but  soon  relapses  into  a  state  of  quietude,  being 
unable  to  remember  impressions  and  connect  them  with  any  train  of 
ideas,  the  faculties  of  memory,  reason,  and  judgment  being  completely 
abolished. 


CEREBRAL  LOCALIZATION  OF  FUNCTION. 

From  experiments  made  upon  animals,  and  from  the  results  of  clinical  and 
post-mortem  observations  upon  men,  it  has  been  shown  that  the  phenomena 
of  organic  and  psychic  life  are  presided  over  by  anatomically  localized 
centers  in  the  brain.  A  knowledge  of  the  position  of  these  centers  becomes 
of  the  highest  importance  in  localizing  the  seat  of  lesions,  thrombi,  hemor- 
rhages, new  growths,  etc. ,  which  show  themselves  in  paralyses,  epilepsies, 
etc.  It  has  not  been  possible  to  thus  localize  all  functions,  and  to  many 
parts  of  the  brain  no  special  use  can  be  assigned.  The  following  are  the 
centers  most  definitely  mapped  out  and  that  are  of  paramount  importance. 

Motor  Centers. — These  are  in  the  cortical  gray  matter,  and  are  ar- 
ranged along  either  side  of  the  fissure  of  Rolando.  This  area  is  known 
as  the  motor  area  or  motor  zone,  stimulation  of  which  is  followed  by  con- 
vulsive movements  of  the  muscles  of  the  opposite  side  of  the  body,  while 
destruction  of  the  gray  matter  of  this  area  is  followed  by  permanent  paral- 
ysis of  the  muscles  of  the  opposite  side.  From  experiments  made  upon 
monkeys,  Ferrier  has  mapped  out  a  number  of  motor  centers  which  he  has 
transferred  to  corresponding  localities  on  the  human  brain.  (See  Fig.  26. ) 
The  descriptive  text  of  the  illustration  renders  his  results  intelligible. 
Pathologic  studies  have  largely  confirmed  his  deductions.  In  a  general 
way  it  maybe  said  that  the  upper  third  of  the  ascending  frontal  and  parietal 
convolutions  about  this  fissure  preside  over  the  movements  of  the  leg  of 
the  opposite  side  of  the  body ;  the  middle  third  controls  the  movements  of 
the  arm  ;  the  upper  part  of  the  inferior  third  is  the  facial  area.  The  lowest 
part  of  the  inferior  third  governs  the  motility  of  the  lips  and  tongue,  and 
this  space,  with  the  posterior  extremity  of  the  third  frontal  convolution, 
constitutes  the  speech  center. 

The  experiments  of  Horsley  and  Schafer  have  enabled  them  to  furnish 
a  new  diagrammatic  representation  of  the  motor  area  and  more  accurately 


CEREBRAL    LOCALIZATION   OF   FUNCTION. 


215 


to  define  the  special  areas  upon  the  lateral  and  mesial  aspects  of  the  brain 
of  the  monkey.  The  boundaries  of  the  general  and  special  areas,  as  deter- 
mined by  these  observers,  will  be  readily  understood  by  an  examination  of 
Figures  27  and  28. 


Fig.  27. — Diagram  of  the  Motor  Areas  on  the  Outer  Surface  of  a  Monkey's 
Brain. — (Horsley  and  Schafer.) 


Fig.  28. — Diagram  of  the  Motor  Areas  on  the  Marginal  Convolution  of  a 
Monkey's  Brain. — {Horsley  and  Schafer.) 

For  diagnostic  purposes  the  motor  areas  for  the  face  and  limbs  have  been 

subdivided  as  follows  : 

I.  The /ace  area  may  be  divided  into  an  upper  part,  comprising  about  one 
third,  and  a  lower  part,  comprising  the  remaining  two  thirds.  In  the 
upper  part  are  centers  governing  the  movements  of  the  muscles  of  the 


216  HUMAN   PHYSIOLOGY. 

opposite  angle  of  the  mouth  and  of  the  lower  face.  The  anterior  portion 
of  the  lower  two  thirds  controls  the  movements  of  the  vocal  cords,  and 
may  be  regarded  as  a  laryngeal  center  ;  the  posterior  portion  governs  the 
opening  and  shutting  of  the  mouth  and  the  protrusion  and  retraction  of 
the  tongue. 

2.  The  upper  limb  area  may  be  subdivided  as  follows  :  The  upper  part 
controls  the  movements  of  the  shoulder  ;  posteriorly  and  below  this  point 
are  centers  for  the  elbow  ;  below  and  anteriorly,  centers  for  the  wrist 
and  finger  movements,  while  lowest  and  posteriorly,  centers  governing  the 
thumb. 

3.  The  leg  area  may  be  subdivided  as  follows :  The  anterior  part,  both  on 
the  mesial  and  lateral  surfaces,  contains  centers  governing  the  hip  and 
thigh  movements ;  in  the  posterior  part  are  centers  for  the  movements  of 
the  leg  and  toes.  The  center  for  the  great  toe  has  been  located  in  the 
paracentral  lobule. 

4.  The  trunk  area,  situated  largely  on  the  mesial  surface,  contains  ante- 
riorly centers  governing  the  rotation  and  arching  of  the  spine,  while 
posteriorly  are  found  centers  governing  movements  of  the  tail  and  pelvis. 

5.  The  head  area,  or  area  for  visual  direction,  contains  centers  excitation 
of  which  causes  "  opening  of  the  eyes,  dilatation  of  the  pupils,  and  turn- 
ing of  the  head  to  the  opposite  side,  with  conjugate  deviation  of  the  eyes 
to  that  side." 

The  centers  of  origin  of  the  nerves  for  the  ocular  muscles  lie  in  the  gray 
matter  of  the  aqueduct  of  Sylvius.  Destruction  of  the  gray  matter  at  these 
points  is  followed  by  paralysis  of  the  muscles  of  the  opposite  side  of  the 
body,  and  morbid  growths,  hemorrhages,  or  thrombi  of  the  vessels  of  the 
part  result  in  abnormal  stimulation  or  in  interference  with  the  functions  cor- 
responding to  the  nature  and  extent  of  the  lesion.  Cerebral  or  Jacksonian 
epilepsy  is  a  result  of  local  cortical  disease. 

Center  for  Speech. — Pathologic  investigations  have  demonstrated  that 
the  left  third  frontal  convolution  is  of  essential  importance  for  speech. 
Adjoining  this  convolution  are  the  centers  controlling  the  motility  of  the 
lips,  tongue,  etc.  In  the  majority  of  cases  the  speech  centers  are  on  the 
left  side  of  the  brain,  though  in  exceptional  cases  they  are  on  the  right 
side,  especially  in  left-handed  persons.  In  deaf  mutes  this  convolution  is 
very  imperfectly  developed,  while  in  monkeys  it  is  quite  rudimentary. 

Lesions  of  the  third  frontal  convolution  on  the  left  side,  if  the  patient  be 
right-handed,  produce  the  various  forms  of  aphasia^  or  the  partial  or  com- 
plete loss  of  the  power  of  articulate  speech. 


CEREBRAL    LOCALIZATION    OF    FUNCTION. 


217 


Aphasia  is  of  many  degrees  and  kinds.  In  ataxic  aphasia  the  patient  is 
unable  to  communicate  his  thoughts  by  words,  there  being  an  inability  to 
execute  the  movements  of  the  mouth,  etc.,  necessary  for  speech.  In 
agraphic  aphasia  there  is  an  inability  to  execute  the  movements  necessary 
for  writing,  though  the  mental  processes  are  retained.  In  the  ataxic  form 
the  lesion  is  in  the  third 
frontal  convolution,  and  in 
the  agraphic  form  it  is  in  the 
arm  center. 

In  amnesic  aphasia  there 
is  a  loss  of  the  memory  of 
words,  the  purest  examples 
of  which  consist  of  the  affec- 
tions known  as  word-deaf- 
ness and  word-blindness.  In 
word -deafness  the  patient  can 
not  understand  vocal  speech, 
though  he  is  capable  of  hear- 
ing other  sounds.  This  con- 
dition is  associated  with  le- 
sion of  the  first  temporal  con- 
volution. In  ivord-blindness 
the  patient  can  not  name  a 
letter  or  a  word  when  printed 
or  written,  though  he  can  see 
all  other  objects.  This  con- 
dition is  associated  with  im- 
pairment of  the  visual  cen- 
ters. 

Figure  29  will  illustrate 
the  conditions  in  the  various 
forms  of  aphasia.  Impres- 
sions are  constantiy  passing 

from  eye  and  ear  to  the  visual  and  auditory  centers  and  are  there  being  regis- 
tered. Commissural  fibers  connect  these  centers  with  the  arm  and  speech 
centers,  which  in  turn  are  connected  by  efferent  fibers  with  the  muscles  of 
the  hand  and  of  the  vocal  apparatus.  Muscular  movements  of  the  eyes,  hand, 
and  mouth  are  also  registered  by  means  of  the  afferent  fibers,  s,  s7,  s". 

Sensory  Centers. — These  are  the  centers  in  which  the  sensory  impres- 
15 


Fig.  29. 


218  HUMAN    PHYSIOLOGY. 

sions  are  coordinated,  and  in  which  they  probably  become  parts  of  our 
consciousness.     The  most  important  are  : 

The  visual  center,  located  in  the  occipital  lobe  and  especially  in  the 
cuneus.  Unilateral  destruction  of  this  area  results  in  hemianopsia,  or 
blindness  of  the  corresponding  halves  of  the  two  retinae.  Destruction  of 
both  occipital  lobes  in  man  results  in  total  blindness.  Stimulation  or  irri- 
tation of  the  visual  center  causes  photopsia,  or  hallucinations  of  sight,  in 
corresponding  halves  of  the  retinae.  There  have  been  instances  of  injury 
of  these  parts  when  sensations  of  color  were  abolished  with  preservation  of 
those  of  space  and  light,  thus  showing  a  special  localization  of  the  color 
center.  Recent  experiments  show  that  the  centers  of  the  two  hemispheres 
are  united,  as  ocular  fatigue  of  an  unused  eye  was  found  to  be  proportional 
to  the  fatigue  of  the  exercised  one. 

The  auditory  centers  are  located  in  the  temporosphenoid  lobes.  Word- 
deafness  is  associated  with  softening  of  these  parts,  and  their  complete 
removal  results  in  deafness. 

The  gustatory  and  olfactojy  centers  are  located  in  the  uncinate  gyrus,  on 
the  inner  side  of  the  temporosphenoid  lobes.  There  does  not  seem  to  be 
any  differentiation,  up  to  this  time,  of  these  two  centers. 

The  center  for  tactile  impressions  was  located  by  Ferrier  in  the  hippo- 
campal  region.  Horsley  and  Schafer  found  that  destructive  lesions  of  the 
gyrus  fornicatus  were  followed  by  hemianesthesia  of  the  opposite  side  of  the 
body,  which  was  more  or  less  marked  and  persistent.  These  observers 
conclude  that  the  limbic  lobe  "is  largely,  if  not  exclusively,  concerned  in 
the  appreciation  of  sensations,  painful  and  tactile." 

The  superior  and  middle  frontal  convolutions  appear  to  be  the  seats  of 
the  reason,  intelligence,  and  will.  Destruction  of  these  parts  is  followed 
by  proportional  hebetude,  without  any  impairment  of  sensation  or  motion. 


SYMPATHETIC   NERVOUS    SYSTEM. 

The  sympathetic  nervous  system  consists  of  a  chain  of  ganglia 
connected  by  longitudinal  nerve  filaments,  situated  on  each  side  of  the 
spinal  column,  running  from  above  downward.  The  two  ganglionic  cords 
are  connected  in  the  interior  of  the  cranium  by  the  ganglion  of  Ribes,  on 
the  anterior  communicating  artery,  and  terminate  in  the  ganglion  impar, 
situated  at  the  top  of  the  coccyx. 

The  chain  of  ganglia  is  divided  into  groups,  and  named  according  to  the 


SYMPATHETIC   NERVOUS   SYSTEM.  219 

location  in  which  they  are  found — viz.,  cranial,  four  in  number;  cervical, 
three  ;  thoracic,  twelve  ;  lumbar,  five  ;  sacral,  five  ;  coccygeal,  one.  Each 
ganglion  consisis  of  a  collection  of  vesicular  nervous  matter,  bundles  of 
non-medullated  nerve-fibers,  embedded  in  a  capsule  of  connective  tissue. 
The  ganglia  are  reinforced  by  motor  and  sensory  fibers  from  the  cerebro- 
spinal nervous  system. 

The  ganglia  have  distinct  nerve-fibers,  from  which  branches  are  dis- 
tributed to  the  glands,  arteries,  and  muscles,  and  to  the  cerebral  and  spinal 
nerves  ;  many  pass,  also,  to  the  visceral  ganglia — e.  g.,  cardiac,  semilunar, 
pelvic,  etc. 

Cephalic  Ganglia. 

1.  The  ophthalmic  or  ciliary  ganglion  is  situated  in  the  orbital  cavity,  pos- 
terior to  the  eyeball ;  it  is  of  small  size  and  of  a  reddish-gray  color ; 
receives  filaments  of  communication  from  the  motor  oculi,  ophthalmic 
branch  of  the  fifth  pair,  and  the  carotid  plexus.  Its  filaments  of  distri- 
bution are  the  ciliary  nerves,  which  consist  of — 

(a)  Motor  fibers  for  the  circular  fibers  of  the  iris  and  ciliary  muscle. 
(3)   Sensory  fibers  for  the  cornea,  iris,  and  associated  parts. 

(c)  Vaso-motor  fibers  for  the  blood-vessels  of  the  choroid,  iris,  and 
retina. 

(d)  Motor  fibers  for  the  dilator  fibers  of  the  iris. 

2.  The  sphenopalatine  or  Meckel's  ganglion,  triangular  in  shape,  is 
situated  in  the  sphenomaxillary  fossa  ;  receives  filaments  from  the  facial 
(Vidian  nerve)  and  the  superior  maxillary  branch  of  the  fifth  nerve.  Its 
filaments  of  distribution  pass  to  the  gums,  the  soft  palate,  and  the  levator 
palati  and  azygos  uvulse  muscles. 

3.  The  otic  or  Arnold's  ganglion  is  of  small  size,  oval  in  shape,  and  situ- 
ated beneath  the  foramen  ovale  ;  receives  a  motor  filament  from  the  facial 
and  sensory  filaments  from  the  glossopharyngeal  and  fifth  nerves  ;  sends 
filaments  to  the  mucous  membrane  of  the  tympanic  cavity  and  to  the 
tensor  tympani  muscle. 

4.  The  submaxillary  ganglion,  situated  in  the  submaxillary  gland,  receives 
filaments  from  the  chorda  tympani,  sensory  filaments  from  the  lingual 
branch  of  the  fifth  nerve,  and  filaments  from  the  sympathetic.  The 
chorda  tympani  nerve  supplies  vaso-dilator  and  secretoiy  fibers  to  the  sub- 
maxillary and  sublingual  glands.  The  fifth  nerve  endows  the  glands  with 
sensibility,  while  the  sympathetic  supplies  secretory  or  trophic  fibers. 

Cervical  Ganglia. 

The  stcperior  cervical  ganglion  is  fusiform  in  shape,  of  a  grayish-red 


220  HUMAN    PHYSIOLOGY. 

color,  and  situated  opposite  the  second  and  third  cervical  vertebrae  ;  it  sends 
branches  to  form  the  carotid  and  cavernous  plexuses,  which  branches  follow 
the  course  of  the  carotid  arteries  to  their  distribution ;  also  sends  branches 
to  join  the  glossopharyngeal  and  pneumogastric,  to  form  the  pharyngeal 
plexus. 

The  middle  cervical  ganglion,  the  smallest  of  the  three,  is  occasionally 
absent ;  it  is  situated  opposite  the  fifth  cervical  vertebra  ;  sends  branches 
to  the  superior  and  inferior  cervical  ganglia  and  to  the  thyroid  artery. 

The  inferior  cervical  ganglion,  irregular  in  form,  is  situated  opposite  the 
last  cervical  vertebra  ;  it  is  frequently  united  with  the  first  thoracic  ganglion. 

The  superior,  middle,  and  inferior  cardiac  nerves,  arising  from  these  cer- 
vical ganglia,  pass  downward  and  forward  to  form  the  deep  and  superficial 
cardiac  plexuses  located  at  the  bifurcation  of  the  trachea,  from  which 
branches  are  distributed  to  the  heart,  coronary  arteries,  etc. 

The  thoracic  ganglia  are  usually  twelve  in  number,  and  are  placed 
against  the  heads  of  the  ribs  behind  the  pleura  ;  they  are  small  in  size 
and  gray  in  color  ;  they  communicate  with  the  cerebro-spinal  nerves  by 
two  filaments,  one  of  which  is  white,  the  other  gray. 

The  great  splanchnic  nerve  is  formed  by  the  union  of  branches  from  the 
sixth,  seventh,  eighth,  and  ninth  ganglia  ;  it  passes  through  the  diaphragm 
to  the  semilunar  ganglion. 

The  lesser  splanchnic  nerve  is  formed  by  the  union  of  filaments  from  the 
tenth  and  eleventh  ganglia,  and  is  distributed  to  the  celiac  plexus. 

The  renal  splanchnic  nerve  arises  from  the  last  thoracic  ganglion  and 
terminates  in  the  renal  plexus. 

The  semilunar  ganglia ,  the  largest  of  the  sympathetic  system,  are  situated 
by  the  side  of  the  celiac  axis  ;  they  send  radiating  branches  to  form  the  solar 
plexus  ;  from  the  various  plexuses,  nerves  follow  the  gastric,  splenic,  he- 
patic, renal,  etc.,  arteries,  into  the  different  abdominal  viscera. 

The  lumbar  ganglia,  four  in  number,  are  placed  upon  the  bodies  of 
the  vertebra  ;  they  give  off  branches,  which  unite  to  form  the  aortic  lumbar 
plexus  and  the  hypogastric  plexus,  and  follow  the  blood-vessels  to  their 
terminations. 

The  sacral  and  coccygeal  ganglia  send  filaments  of  distribution  to 
all  the  blood-vessels  of  the  pelvic  viscera. 

Properties  and  Functions.— The  sympathetic  nerve  possesses  both 
sensibility  and  the  power  of  exciting  motion,  but  these  properties  are  much 
less  decided  than  in  the  cerebro-spinal  system.     Irritation  of  the  ganglia 


SYMPATHETIC  NERVOUS   SYSTEM.  221 

does  not  produce  any  evidence  of  pain  until  some  time  has  elapsed.  If 
caustic  soda  be  applied  to  the  semilunar  ganglia,  or  a  galvanic  current  be 
passed  through  the  splanchnic  nerve,  no  instantaneous  effect  is  noticed,  as 
in  the  case  of  the  cerebro-spinal  nerves  ;  but  in  the  course  of  a  few  seconds 
a  slow,  progressive  contraction  of  the  muscular  coat  of  the  intestines  is 
established,  which  continues  for  some  time  after  the  irritation  has  been 
removed.  Division  of  the  sympathetic  nerve  in  the  neck  is  followed  by  a 
vascular  congestion  of  the  parts  above  the  section  on  the  corresponding  side, 
attended  by  an  increase  in  the  temperature ;  not  only  is  there  an  increase  in 
the  amount  of  blood,  but  the  rapidity  of  the  blood  current  is  very  much 
accelerated  and  the  blood  in  the  veins  becomes  of  a  brighter  color.  Gal- 
vanization of  the  upper  end  of  the  divided  nerve  causes  all  the  preceding 
phenomena  to  disappear  ;  the  congestion  decreases,  the  temperature  falls, 
and  the  venous  blood  becomes  dark  again. 

The  sympathetic  exerts  a  similar  influence  upon  the  circulation  of  the 
limbs  and  the  glandular  organs ;  destruction  of  the  first  thoracic  ganglion 
and  division  of  the  nerves  forming  the  lumbar  and  sacral  plexuses  are  fol- 
lowed by  a  dilatation  of  the  vessels,  an  increased  rapidity  of  the  circula- 
tion, and  an  elevation  of  temperature  in  the  anterior  and  posterior  limbs  ; 
galvanization  of  the  peripheral  ends  of  these  nerves  causes  all  of  these  phe- 
nomena to  disappear.  Division  of  the  splanchnic  nerve  causes  a  dilatation 
of  the  blood-vessels  of  the  intestine. 

These  phenomena  of  the  sympathetic  nervous  system  are  dependent  upon 
the  presence  of  vaso-motor  nerves,  which,  under  normal  circumstances, 
exert  a  tonic  influence  upon  the  blood-vessels.  These  nerves,  derived 
from  the  cerebro-spinal  system  and  the  medulla  oblongata,  leave  the  spinal 
cord  by  the  rami  comtnunicantes,  enter  the  sympathetic  ganglia,  and  finally 
terminate  in  the  muscular  walls  of  the  blood-vessels. 

Sleep  is  a  periodic  condition  of  the  nervous  system  in  which  there  is  a 
partial  or  complete  cessation  of  the  activities  of  the  higher  nerve  centers. 
The  cause  of  sleep  is  a  diminution  in  the  quantity  of  blood,  occasioned  by 
a  contraction  of  the  smaller  arteries  under  the  influence  of  the  vaso-motor 
nerves. 

During  the  waking  state  the  brain  undergoes  a  physiologic  waste,  as  a 
result  of  the  exercise  of  its  functions ;  after  a  certain  length  of  time  its 
activities  become  enfeebled,  and  a  period  of  repose  ensues,  during  which  a 
regeneration  of  its  substance  takes  place. 

When  the  brain  becomes  enfeebled,  there  is  a  diminished  molecular 
activity  and  an  accumulation  of  waste  products  ;  under  these  circumstances 


222  HUMAN    PHYSIOLOGY. 

it  ceases  to  dominate  the  medulla  oblongata  and  the  spinal  cord.  These 
centers  then  act  more  vigorously,  and  diminish  the  caliber  of  the  cerebral 
blood-vessels  through  the  action  of  the  vaso-motor  nerves,  producing  a 
condition  of  physiologic  anemia  and  sleep  ;  during  this  state  waste  products 
are  removed,  force  is  stored  up,  nutrition  is  restored,  and  waking  finally 
occurs. 


THE    SENSE    OF   TOUCH. 

The  sense  of  touch  is  a  modification  of  general  sensibility,  and  is  located 
in  the  skin,  which  is  especially  adapted  for  this  purpose  on  account  of  the 
number  of  nerves  and  papillary  elevations  it  possesses.  The  structures  of 
the  skin  and  the  modes  of  termination  of  the  sensory  nerves  have  already 
been  considered. 

The  tactile  sensibility  varies  in  acuteness  in  different"  portions  of  the 
body,  being  most  marked  in  those  regions  in  which  the  tactile  corpuscles 
are  most  abundant — e.  g.,  the  palmar  surface  of  the  third  phalanges  of 
the  fingers  and  thumb. 

The  relative  sensibility  of  different  portions  of  the  body  has  been  ascer- 
tained by  means  of  a  pair  of  compasses  :  the  points  of  the  instrument  being 
guarded  by  cork,  it  was  then  determined  how  closely  they  could  be  brought 
together,  and  yet  be  felt  at  two  different  points.  The  following  are  some 
of  the  measurements : 

Point  of  tongue, ^  of  a  line. 

Palmar  surface  of  third  phalanx, I  line. 

Red  surface  of  lips, 2  lines. 

Palmar  surface  of  metacarpus, 3    " 

Tip  of  the  nose, 3     " 

Part  of  lips  covered  by  skin, 4    " 

Palm  of  hand, .    .    5     " 

Lower  part  of  forehead,    .    .        10    " 

Back  of  hand, 14    " 

Dorsum  of  foot, 1 8    " 

Middle  of  the  thigh, .    .    .  30    " 

The  sense  of  touch  communicates  to  the  mind  the  idea  of  resistance  only, 
and  the  varying  degrees  of  resistance  offered  to  the  sensory  nerves  enable 
us  to  estimate,  with  the  aid  of  the  muscular  sense,  the  qualities  of  hardness 
or  softness  of  external  objects.  The  idea  of  space  or  extension  is  obtained 
when  the  sensory  surface  or  the  external  object  changes  its  place  in  regard 


THE   SENSE   OF   TASTE.  223 

to  the  other ;  the  character  of  the  surface,  its  roughness  or  smoothness,  is 
estimated  by  the  impressions  made  upon  the  tactile  papilke. 

Appreciation  of  Temperature. — The  general  surface  of  the  body  is  more 
or  less  sensitive  to  differences  of  temperature,  though  this  sensation  is 
separate  from  that  of  touch  ;  whether  there  are  nerves  especially  adapted 
for  the  conduction  of  this  sensation  has  not  been  fully  determined.  Under 
pathologic  conditions,  however,  the  sense  of  touch  may  be  abolished,  while 
the  appreciation  of  changes  in  temperature  may  remain  normal. 

The  cutaneous  surface  varies  in  its  sensibility  to  temperature  in  different 
parts  of  the  body,  and  depends,  to  some  extent,  upon  the  thickness  of  the 
skin,  exposure,  habit,  etc.  ;  the  inner  surface  of  the  elbow  is  more  sensitive 
to  changes  in  temperature  than  the  outer  portion  of  the  arm  ;  the  left  hand 
is  more  sensitive  than  the  right,  the  mucous  membrane  less  so  than  the 
skin. 

Excessive  heat  or  cold  has  the  same  effect  upon  the  sensibility  ;  the  tem- 
peratures most  readily  appreciated  are  those  between  500  F.  and  115°  F. 

The  sensations  of  pain  and  tickling  appear  to  be  conducted  to  the  brain, 
also,  by  nerves  different  from  those  of  touch  ;  in  abnormal  conditions  the 
appreciation  of  pain  may  be  entirely  lost  while  touch  remains  unimpaired. 


THE    SENSE    OF   TASTE. 

The  sense  of  taste  is  localized  mainly  in  the  mucous  membrane  cover- 
ing the  superior  surface  of  the  tongue. 

The  tongue  is  situated  in  the  floor  of  the  mouth  ;  its  base  is  directed 
backward  and  is  connected  with  the  hyoid  bone  and  by  numerous  muscles 
with  the  epiglottis  and  soft  palate  ;  its  apex  is  directed  forward  against  the 
posterior  surface  of  the  teeth. 

The  substance  of  the  tongue  is  made  up  of  intrinsic  muscle-fibers,  the 
linguales  ;  it  is  attached  to  surrounding  parts,  and  its  various  movements  are 
performed  by  the  extrinsic  muscles — e.  g.,  styloglossus,  geniohyoglossus,  etc. 

The  mucous  membrane  covering  the  tongue  is  continuous  with  that  lining 
the  commencement  of  the  alimentary  canal,  and  is  furnished  with  vascular 
and  nervous  papillae. 

The  papillce  are  analogous  in  their  structure  to  those  of  the  skin,  and  are 
distributed  over  the  dorsum  of  the  tongue,  giving  it  its  characteristic 
roughness. 


224  HUMAN  PHYSIOLOGY. 

There  are  three  principal  varieties — 

1 .  The  filiform  papillae  are  most  numerous,  and  cover  the  anterior  two 
thirds  of  the  tongue  ;  they  are  conic  or  filiform  in  shape,  often  pro- 
longed into  filamentous  tufts,  of  a  whitish  color,  and  covered  by  horny 
epithelium. 

2.  The.  fungiform  papilla  are  found  chiefly  at  the  tip  and  sides  of  the 
tongue ;  they  are  larger  than  the  preceding,  and  may  be  recognized  by 
their  deep  red  color. 

3.  The  circumvallate  papillce  are  rounded  eminences,  from  eight  to  ten  in 
number,  situated  at  the  base  of  the  tongue,  where  they  form  a  V-shaped 
figure.  They  are  quite  large,  and  consist  of  a  central  projection  of 
mucous  membrane,  surrounded  by  a  wall,  or  circumvallation,  from  which 
they  derive  their  name. 

The  taste-beakers,  supposed  to  be  the  true  organs  of  taste,  are  flask- 
like-bodies, ovoid  in  form,  about  j^  of  an  inch  in  length,  situated  in  the 
epithelial  covering  of  the  mucous  membrane,  on  the  circumvallate  papillae. 
They  consist  of  a  number  of  fusiform,  narrow  cells,  which  are  curved  so  as  to 
form  the  walls  of  this  flask-like  body ;  in  the  interior  are  elongated  cells, 
with  large,  clear  nuclei,  the  taste-cells. 

Nerves  of  Taste. — The  chorda  tympani  nerve,  a  branch  of  the  facial, 
after  leaving  the  cavity  of  the  tympanum,  joins  the  third  division  of  the  fifth 
nerve  between  the  two  pterygoid  muscles,  and  then  passes  forward  in  the 
lingual  branches,  to  be  distributed  to  the  mucous  membrane  of  the  anterior 
two  thirds  of  the  tongue.  Division  or  disease  of  this  nerve  is  followed  by 
a  loss  of  taste  in  the  part  to  which  it  is  distributed. 

The  glossopharyngeal  enters  the  tongue  at  the  posterior  border  of  the 
hyoglossus  muscle,  and  is  distributed  to  the  mucous  membrane  of  the  base 
and  sides  of  the  tongue,  fauces,  etc. 

The  lingual  branch  of  the  trifacial  nerve  endows  the  tongue  with  gen- 
eral sensibility  ;  the  hypoglossal  endows  it  with  motion. 

The  nerves  of  taste  in  the  superficial  layer  of  the  mucous  membrane  form 
a  fine  plexus,  from  which  branches  pass  to  the  epithelium  and  penetrate 
it ;  others  enter  the  taste-beakers,  and  are  directly  connected  with  the 
taste -cells. 

The  seat  of  the  sense  of  taste  has  been  shown  by  experiment  to  be  the 
whole  of  the  mucous  membrane  over  the  dorsum  of  the  tongue,  soft  palate, 
fauces,  and  upper  part  of  the  pharynx. 

The  sense  of  taste  enables  us  to  distinguish  the  savor  of  substances 


THE  SENSE  OF  SMELL.  225 

introduced  into  the  mouth,  which  faculty  is  different  from  tactile  sensibility, 
The  sapid  qualities  of  substances  appreciated  by  the  tongue  are  designated 
as  bitter,  sweet,  alkaline,  sour,  salt,  etc. 

The  essential  conditions  for  the  production  of  the  impressions  of  taste 
are  : 

1.  A  state  of  solubility  of  the  food. 

2.  A  free  secretion  of  the  saliva,  and 

3.  Active  movements  on  the  part  of  the  tongue,  exciting  pressure  against 
the  roof  of  the  mouth,  gums,  etc.,  thus  aiding  the  solution  of  various 
articles  and  their  osmosis  into  the  lingual  papillae. 

Sapid  substances,  when  in  a  state  of  solution,  pass  into  the  interior  of 
the  taste-beakers,  and  come  into  contact,  through  the  medium  of  the  taste- 
cells,  with  the  terminal  filaments  of  the  gustatory  nerves. 


THE  SENSE  OF  SMELL. 

The  sense  of  smell  is  located  in  the  mucous  membrane  lining  the  upper 
part  of  the  nasal  cavity,  in  which  the  olfactory  nerves  are  distributed. 

The  nasal  fossae  are  two  cavities,  irregular  in  shape,  separated  by  the 
vomer,  the  perpendicular  plate  of  the  ethmoid  bone,  and  the  triangular  car- 
tilage. They  open  anteriorly  and  posteriorly  by  the  anterior  and  posterior 
nares,  the  latter  communicating  with  the  pharynx.  They  are  lined  by 
mucous  membrane,  of  which  the  only  portion  capable  of  receiving  odorous 
impressions  is  the  part  lining  the  upper  one  third  of  the  fossse. 

The  olfactory  nerves,  arising  by  three  roots  from  the  posterior  and 
inferior  surface  of  the  anterior  lobes,  pass  forward  to  the  cribriform  plate 
of  the  ethmoid  bone,  where  they  each  expand  into  an  oblong  body,  the 
olfactory  bulb.  From  its  under  surface  from  fifteen  to  twenty  filaments 
pass  downward  through  the  foramina,  to  be  distributed  to  the  olfactory 
mucous  membrane,  where  they  terminate  in  long,  delicate,  spindle-shaped 
cells,  the  olfactory  cells,  situated  between  the  ordinary  epithelial  cells. 

The  olfactory  bulbs  are  the  centers  in  which  odorous  impressions  are 
perceived  as  sensations,  destruction  of  these  bulbs  being  attended  by  an 
abolition  of  the  sense  of  smell. 

In  animals  which  possess  an  acute  sense  of  smell  there  is  a  correspond- 
ing increase  in  the  development  of  the  olfactory  bulbs. 


226  HUMAN   PHYSIOLOGY. 

The  essential  conditions  for  the  sense  of  smell  are — 

1.  A  special  nerve  center  capable  of  receiving  impressions  and  transform- 
ing them  into  odorous  sensations. 

2.  Emanations  from  bodies  which  are  in  a  gaseous  or  vaporous  condition. 

3.  The  odorous  emanations  must  be  drawn  freely  through  the  nasal  fossae  ; 
if  the  odor  be  very  faint,  a  peculiar  inspiratory  movement  is  made,  by 
which  the  air  is  forcibly  brought  into  contact  with  the  olfactory  filaments. 
The  secretions  of  the  nasal  fossae  probably  dissolve  the  odorous  particles. 
Various  substances,  as  ammonia,  horseradish,  etc. ,  excite  the  sensibility 

of  the  mucous  membrane  ;  this  must  be  distinguished  from  the  perception 
of  true  odors. 


THE  SENSE  OF  SIGHT. 

The  Eyeball. — The  eyeball,  or  organ  of  vision,  is  situated  at  the  fore 
part  of  the  orbital  cavity  and  is  supported  by  a  cushion  of  fat ;  it  is  protected 
from  injury  by  the  bony  walls  of  the  cavity,  the  lids,  and  the  lashes,  and  is  so 
situated  as  to  permit  of  an  extensive  range  of  vision.  The  eyeball  is  loosely 
held  in  position  by  a  fibrous  membrane,  the  capstde  of  Tenon,  which  is 
attached  on  the  one  hand  to  the  eyeball  itself  and  on  the  other  to  the  walls 
of  the  cavity.  Thus  suspended,  the  eyeball  is  capable  of  being  moved  in 
any  direction  by  the  contraction  of  the  muscles  attached  to  it. 

Structure. — The  eyeball  is  spheroid  in  shape  and  measures  about  T9^  of 
an  inch  in  its  anteroposterior  diameter,  and  a  little  less  in  its  transverse 
diameter.  When  viewed  in  profile,  it  is  seen  to  consist  of  the  segments  of 
two  spheres,  of  which  the  posterior  is  the  larger,  occupying  five  sixths,  and 
the  anterior  the  smaller,  occupying  one  sixth,  of  the  ball. 

The  eye  is  made  up  of  several  membranes,  concentrically  arranged, 
within  which  are  inclosed  the  refracting  media  essential  to  vision.  These 
membranes,  enumerated  from  without  inward,  are — 

1 .  The  sclerotic  and  cornea. 

2.  The  choroid  and  iris. 

3.  The  retina. 

The  refracting  media  are  the  aqueous  humor,  the  crystalline  lens,  and 
the  vitreous  humor. 

The  Sclerotic  and  Cornea. — The  sclerotic  is  the  opaque  fibrous  mem- 
brane covering  the  posterior  five  sixths  of  the  ball.  It  is  composed  of 
connective  tissue  arranged  in  layers,  which  run  both  transversely  and 
longitudinally  ;  it  is  pierced  posteriorly  by  the  optic  nerve  about  Txff  of  an 


THE   SENSE   OF   SIGHT.  227 

inch  internal  to  the  optic  axis.  The  sclerotic,  by  its  density,  gives  form  to 
the  eye  and  protects  the  delicate  structures  within  it,  and  serves  for  the 
attachment  of  the  muscles  by  which  the  ball  is  moved. 

The  cornea  is  a  transparent  non-vascular  membrane  covering  the  anterior 
one  sixth  of  the  eyeball.  It  is  nearly  circular  in  shape  and  is  continuous 
at  the  circumference  with  the  sclerotic,  from  which  it  can  not  be  separated. 
The  substance  of  the  cornea  is  made  up  of  thin  layers  of  delicate,  trans- 
parent fibrils  of  connective  tissue,  more  or  less  united  ;  between  these  layers 
are  found  a  number  of  intercommunicating  lymph-spaces,  lined  by  endothe- 
lium, which  are  in  connection  with  lymphatics.  Leukocytes  or  lymph- 
corpuscles  are  often  found  in  these  spaces.  The  anterior  surface  of  the 
cornea  is  covered  by  several  layers  of  nucleated  epithelium,  which  rest 
upon  a  structureless  membrane  known  as  the  anterior  elastic  lamina. 
The  posterior  surface  is  covered  by  a  similar  membrane,  the  membrane  of 
Descemet,  which  at  its  periphery  becomes  continuous  with  the  iris ;  it  is 
also  covered  by  a  layer  of  epithelial  cells.  At  the  junction  of  the  cornea 
and  sclerotic  is  found  a  circular  groove,  the  canal  of  Schlemm. 

The  choroid,  the  iris,  the  ciliary  muscle,  and  the  ciliary  processes 
together  constitute  the  second  or  middle  coat  of  the  eyeball. 

The  choroid  is  a  dark  brown  membrane  which  extends  forward  nearly 
to  the  cornea,  where  it  terminates  in  a  series  of  folds,  the  ciliary  processes. 
In  its  structure  the  choroid  is  highly  vascular,  consisting  of  both  arteries 
and  veins.  Externally  it  is  connected  with  the  sclerotic  by  connective 
tissue  ;  internally  it  is  lined  by  a  layer  of  hexagonal  pigment  cells,  which, 
though  usually  classed  as  belonging  to  the  choroid,  is  now  known  to  belong, 
embryologically  and  physiologically,  to  the  retina.  From  without  inward 
may  be  distinguished  the  following  layers  : 

1.  The  lamina  suprachoroidea. 

2.  The  elastic  layer  of  Sattler,  consisting  of  two  endothelial  layers. 

3.  The  chorio-capillaris,  choroid  proper,  or  membrane  of  Ruysch — a  thick, 
elastic  network  of  arterioles  and  capillaries  lying  within  the  outer  layer 
of  veins  and  arteries  called  the  vense  vorticosse. 

4.  The  lamina  vitrea,  or  internal  limiting  membrane. 

The  choroid  with  its  contained  blood-vessels  bears  an  important  relation 
to  the  nutrition  of  the  eye  ;  it  provides  for  the  blood-supply  and  for  drain- 
age from  the  body  of  the  eye,  and  presents  a  uniform  and  high  temperature 
to  the  retina. 

The  iris  is  the  circular,  variously  colored  membrane  placed  in  the 
anterior  portion  of  the  eye  just  behind  the  cornea.     It  is  perforated  a  little 


228 


HUMAN  PHYSIOLOGY. 


to  the  nasal  side  of  the  center  by  a  circular  opening,  the  pupil.  The  outer 
or  circumferential  border  is  connected  with  the  cornea,  ciliary  muscle,  and 
ciliary  processes  ;  the  free  inner  edge  forms  the  boundary  of  the  pupil,  the 
size  of  which  is  constantly  changing.  The  framework  of  the  iris  is  com- 
posed of  connective  tissue  blood-vessels,  muscle-fibers  and  pigmented 
connective-tissue  corpuscles.  The  anterior  surface  is  covered  with  a  layer 
of  ephithelial  cells  continuous  with  those  covering  the  posterior  surface  of 
the  cornea ;  the  posterior  surface  is  lined  by  a  limiting  membrane  bearing 
pigment  epithelial  cells  continuous  with  those  of  the  choroid.     The  various 


-   f 


Fig.   30. — Sclerotic   Coat  removed  to   show  Choroid    Ciliary   Muscle,  and 
Nerves. — {Frojn  Holden's  "Anatomy.") 


a.    Sclerotic  coat. 


b.    Veins  of  the  choroid.       c.   Ciliary  nerves,     d.   Veins  of  the 
choroid,     e.  Ciliary  muscle,    f.  Iris. 


colors  which  the  iris  assumes  in  different  individuals  depend  upon  the 
quantity  and  disposition  of  the  pigment  granules. 

The  muscle-fibers  of  the  iris,  which  are  of  the  non-striated  variety,  are 
arranged  in  two  sets — the  sphincter  and  dilator. 

The  sphincter  pupillce  is  a  circular,  flat  band  of  muscle-fibers  surrounding 
the  pupil  close  to  its  posterior  surface  ;  by  its  contraction  and  relaxation 
the  pupil  is  diminished  or  increased  in  size.  The  dilatator  pupillce  consists 
of  a  thin  layer  of  fibers  arranged  in  a  radiate  manner  ;  at  the  margin  of  the 
pupil  they  blend  with  those  of  the  sphincter  muscle,  while  at  the  outer 
border  they  arch  to  form  a  circular  muscular  layer. 

The   ciliary  muscle  is  a  gray,   circular  band,    consisting   of  unstriped 


THE   SENSE   OF   SIGHT.  229 

muscle-fibers  about  y1^  of  an  inch  long  running  from  before  backward. 
It  is  attached  anteriorly  to  the  inner  surface  of  the  sclerotic  and  cornea,  and 
posteriorly  to  the  choroid  coat  opposite  the  ciliary  processes.  At  the  an- 
terior border  of  the  radiating  fibers  and  internally  are  found  bundles  of 
circular  muscle-fibers,  constituting  the  anntdar  muscle  of  Miiller.  The 
ciliary  muscle  thus  consists  of  two  sets  of  fibers,  a  radiating  and  a  circular, 
both  of  which  are  concerned  in  effecting  a  change  in  the  convexity  of  the 
lens  in  the  accommodation  of  the  eye  to  near  vision. 

The  retina  forms  the  internal  coat  of  the  eye.  In  the  fresh  state  it  is  a 
delicate,  transparent  membrane  of  a  pink  color,  but  after  death  soon 
becomes  opaque  ;  it  extends  forward  almost  to  the  ciliary  processes,  where 
it  terminates  in  an  indented  border,  the  ora  serrata.  In  the  posterior  part 
of  the  retina,  at  a  point  corresponding  to  the  axis  of  vision,  is  a  yellow  spot, 
the  macula  lulea,  which  is  somewhat  oval  in  shape  and  tinged  with  yellow 
pigment.  It  presents  in  its  center  a  depression,  the  fovea  centralis,  cor- 
responding to  a  decrease  in  thickness  of  the  retina  ;  about  y1^  of  an  inch  to 
the  inner  side  of  the  macula  is  the  point  of  entrance  of  the  optic  nerves 
The  arteria  centralis  retince  pierces  the  optic  nerve  near  the  sclerotic,  runs 
forward  in  its  substance,  and  is  distributed  in  the  retina  as  far  forward  as 
the  ciliary  processes. 

The  retina  is  remarkably  complex,  consisting  of  ten  distinct  layers,  from 
within  outward,  supported  by  connective  tissue.  These  are  as  follows — 
viz.  : 

1.  Membrana  limitans  interna. 

2.  Fibers  of  optic  nerve. 

3.  Layers  of  ganglionic  corpuscles. 

4.  Molecular  layer. 

5.  Internal  granular  layer. 

6.  Molecular  layer. 

7.  External  granular  layer. 

8.  Membrana  limitans  externa. 

9.  Jacobson's  membrane,  or  layer  of  rods  and  cones. 
10.  The  layer  of  pigment  cells. 

The  most  important  of  these,  however,  is  the  layer  of  rods  and  cones  in 
the  external  portion  of  the  retina.  The  rods  are  straight,  elongated  cylin- 
ders extending  through  the  entire  thickness  of  Jacobson'  s  membrane.  They 
consist  of  an  external  portion,  which  is  clear,  homogeneous,  and  highly 
refracting,  and  of  an  internal  portion,  which  is  slightly  granular  and  less 
refractive ;  the  outer  end  of  each  rod  is  in  direct  contact  with  the  pig- 


230  HUMAN    PHYSIOLOGY. 

ment  epithelium  lining  the  choroid,  while  the  inner  end,  tapering  to  a 
fine  thread,  pierces  the  external  limiting  membrane  and  passes  into  the 
external  granular  layer.  The  cones  consist  also  of  two  portions,  the  inner 
of  which  is  somewhat  thicker  than  the  rod  and  rests  upon  the  limiting 
membrane ;  the  outer  portion  tapers  to  a  fine  point,  which  is  known  as  the 
cone-style.  The  cones,  as  a  rule,  are  somewhat  shorter  than  the  rods. 
The  proportion  of  rods  to  cones  varies  in  different  parts  of  the  retina,  though 
there  are  on  an  average  about  fourteen  rods  to  one  cone.  In  the  macula 
lutea,  where  vision  is  most  acute,  the  rods  are  almost  entirely  absent,  cones 
alone  being  present.  All  the  retinal  elements  at  this  point  are  changed. 
The  nerve-fiber  layer  is  absent,  the  axis-cylinders  radiating  in  such  a  man- 
ner as  to  leave  the  spot  free  from  their  covering.  The  remaining  layers  are 
all  thinned  and  the  stroma  is  reduced  to  a  minimum.  The  optic  nerve, 
after  passing  forward  from  the  brain,  penetrates  in  succession  the  sclerotic, 
choroid,  and  retina  ;  the  nerve-fibers  then  spread  out  over  the  anterior  sur- 
face of  the  retina  and  become  connected  with  the  large  ganglionic  cells, 
the  third  layer  of  the  retina. 

The  number  of  optic  nerve-fibers  in  the  retina  is  estimated  to  be  about 
800,000,  and  for  each  fiber  there  are  about  seven  cones,  one  hundred  rods, 
and  seven  pigment  cells.  The  points  of  the  rods  and  cones  are  directed 
toward  the  choroid,  or  away  from  the  entering  light,  and  dip  into  the  pig- 
ment layer.  They,  with  the  pigment  layer,  are  the  intermediating  ele- 
ments in  the  change  of  the  ethereal  vibrations  into  nerve  force ;  out  of 
these  nerve  vibrations  the  brain  fashions  the  sensations  of  light,  form,  and 
color. 

The  vitreous  humor,  which  supports  the  retina,  is  the  largest  of  the  re- 
fracting media  ;  it  is  globular  in  form  and  constitutes  about  four  fifths  of 
the  ball ;  it  is  hollowed  out  anteriorly  for  the  reception  of  the  crystalline 
lens.  The  outer  surface  of  the  vitreous  is  covered  by  a  delicate,  transparent 
membrane,  termed  the  hyaloid  membrane,  which  serves  to  maintain  its 
globular  form. 

The  aqueous  humor,  found  in  the  anterior  chamber  of  the  eye,  is  a  clear 
alkaline  fluid,  having  a  specific  gravity  of  1003-1009.  It  is  secreted  most 
probably  by  the  blood-vessels  of  the  iris  and  ciliary  processes.  It  passes 
from  the  interior  of  the  eye,  through  the  canal  of  Schlemm  and  the  meshes 
at  the  base  of  the  iris,  into  the  anterior  circular  vein. 

The  crystalline  lens,  inclosed  within  its  capsule,  is  a  transparent  bicon- 
vex body,  situated  just  behind  the  iris  and  resting  in  the  depression  in  the 
anterior  part  of  the  vitreous.     The  two  convexities  are  not  quite  alike,  the 

0 

curvature  of  the  posterior  surface  being  slightly  greater  than  that  of  the  an- 


THE   SENSE   OF   SIGHT.  231 

terior.     The  lens  measures  about  \  of  an  inch  in  the  transverse  diameter 
and  £  of  an  inch  in  the  anteroposterior  diameter. 

The  suspensory  ligament,  by  which  the  lens  is  held  in  position,  is  a  firm, 
transparent  membrane,  united  to  the  ciliary  processes.  A  short  distance 
beyond  its  origin  it  splits  into  two  layers,  the  anterior  of  which  is  inserted 
into  the  capsule  of  the  lens  and  blends  with  it ;  the  posterior,  passing  inward 
behind  the  lens,  becomes  united  to  its  capsule.  The  anterior  layer  pre- 
sents a  series  of  foldings,  zone  of  Zinn,  which  are  inserted  into  the  inter- 
vals of  the  folds  of  the  ciliary  processes.  The  triangular  space  between  the 
two  layers  is  the  canal  of  Petit. 

Blood-vessels  and  Nerves. — The  structures  composing  the  eyeball 
are  supplied  with  blood  by  the  long  and  short  ciliary  arteries,  branches  of 
the  ophthalmic ;  they  pierce  the  sclerotic  at  various  points  and  are  ulti- 
mately distributed  to  all  tissues  within  the  ball. 

The  nerve-supply  comes  largely  from  the  ophthalmic  or  ciliary  ganglion. 
This  is  a  small  body,  situated  in  the  posterior  part  of  the  orbit ;  it  receives 
motor  fibers  from  a  branch  of  the  motor  oculi,  or  third  nerve  ;  a  sensory 
branch  from  the  ophthalmic  division  of  the  fifth  nerve,  and  fibers  from  the 
cavernous  plexus  of  the  sympathetic.  From  the  anterior  border  of  the 
ganglion  proceed  the  ciliary  nerves,  which,  entering  the  eyeball,  endow  its 
structures  with  motion  and  sensation. 

The  Eyeball  a  Living  Camera  Obscura. — The  eyeball  may  be  com- 
pared in  a  general  way  to  a  camera  obscura.  The  anatomic  arrangement 
of  its  structures  reveals  many  points  of  similarity.  The  sclerotic  and  choroid 
\nay  be  compared  with  the  walls  of  the  chamber  ;  the  combined  refractive 
media,  cornea,  aqueous  }  -mor,  lens,  and  vitreous  humor,  to  the  lens  for 
focusing  the  rays  of  light ;  the  retina,  to  the  sensitive  plate  receiving  the 
image  formed  at  the  focal  point ;  the  iris,  to  the  diaphragm,  which,  by 
cutting  off  the  marginal  rays,  prevents  spheric  aberration  and  at  the  same 
time  regulates  the  amount  of  light  entering  the  eye  ;  the  ciliary  muscle,  to 
the  adjusting  screw,  by  which  distinct  images  are  thrown  upon  the  retina  in 
spite  of  varying  distances  of  the  object  from  which  the  light  rays  emanate. 
The  structures  just  enumerated  are  those  essential  for  normal  vision. 

The  relationship  of  the  various  structures  composing  the  eyeball  is  shown 
in  Figure  31. 

The  dioptric  or  refracting  apparatus,  by  which  the  rays  of  light  enter- 
ing the  eye  are  so  manipulated  as  to  produce  an  image  on  the  retina,  con- 
sists of  the  cornea,  aqueous  humor,  crystalline  lens,  and  vitreous  humor.  A 
ray  of  light  in  passing  through  each  of  these  media  will  undergo  refraction 


232 


HUMAN   PHYSIOLOGY. 


at  their  surfaces  and  ultimately  be  brought  to  a  focus  at  the  retina.  Inas- 
much as  the  two  surfaces  of  the  cornea  are  parallel  and  its  refractive  power 
practically  the  same  as  the  aqueous  humor,  the  media  may  be  reduced  to 
three — viz. : 

1.  Cornea  and  aqueous  humor. 

2.  The  lens. 

3.  The  vitreous  humor. 


Fig.    31. — Diagram    of    a    Vertical    Section    of    the    Eye. — {From  Holdens, 

"  Anatomy.") 

1.  Anterior  chamber  filled  with  aqueous  humor.  2.  Posterior  chamber.  3  Canal  of 
Petit,  a.  Hyaloid  membrane,  b.  Retina  (dotted  line),  c.  Choroid  coat  (black 
line),  d.  Sclerotic  coat.  e.  Cornea,  f.  Iris.  g.  Ciliary  processes,  h.  Canal  of 
Schlemm  or  Fontana.     z.  Ciliary  muscle. 


The  refracting  surfaces  may  also  be  reduced  to  three — viz.  : 

1.  Anterior  surface  of  the  cornea. 

2.  Anterior  surface  of  lens. 

3.  Posterior  surface  of  lens. 

The  refraction  effected  by  the  cornea  is  very  great,  owing  to  the  passage 
of  the  light  from  the  air  into  a  comparatively  dense  medium,  and  is  sufficient 
of  itself  to  bring  parallel  rays  of  light  to  a  focus  about  ten  millimeters  behind 
the  retina.  This  would  be  the  condition  in  an  eye  in  which  the  lens  was 
congenitally  absent.  Perfect  vision  requires,  however,  that  the  convergence 
of  the  light  shall  be  great  enough  to  allow  the  image  to  fall  upon  the  retina. 


THE    SENSE   OF   SIGHT. 


233 


This  is  accomplished  by  the  crystalline  lens,  a  body  denser  than  the  cornea 
and  possessing  a  higher  refractive  power.  The  manner  in  which  a  bicon- 
vex lens  focuses  both  parallel  and  divergent  rays  is  shown  in  figures  32 
and  33. 

The  function  of  the  crystalline  lens,  therefore,  is  to  focus  the  rays  of  light 
with  the  formation  of  an  image  on  the  retina. 

The  retinal  image  corresponds  in  all  respects  to  the  object  from  which 
the  light  proceeds.  The  existence  of  this  image  can  be  demonstrated  by 
removing  from  the  eye  of  a  recently  killed  animal  a  circular  portion  of  the 
sclerotic  and  choroid  posteriorly,  and  then  placing  at  the  proper  distance  in 


Fig.  32. — Diagram  showing  the  Course  of  Parallel  Rays  of  Light  from 
A,  in  their  Passage  through  a  Biconvex  Lens,  L,  in  which  they  are 
so  Refrated  as  to  Bind  Toward  and  Come  in  a  Focus  at  a  Point,  F. 
—  {Fro?)i  Yeo's  " Te.xf-book  of  Physiology."") 


Fig.  33. — Diagram  showing  the  Course  of  Diverging  Rays  which  are  Bent 
to  a  Point  Further  from  the  Lens  than  the  Parallel  Rays  in  Pre- 
ceding Figure. — (  Yeo's  "  Text-book  of  Physiology.") 


front  of  the  cornea  a  lighted  candle  ;  an  inverted  image  of  the  candle  will 
be  seen  upon  the  retina.  The  size  of  the  retinal  image  depends  upon  the 
visual  angle,  which  in  turn  depends  upon  the  size  of  the  object  and  its  dis- 
tance from  the  eye.  At  a  distance  of  15.2596  meters  the  image  of  an  object 
one  meter  high  would  be  one  millimeter,  or  a  thousand  times  smaller  than 
the  object. 

Accommodation. — By  accommodation  is  understood  the  power  which 
the  eye  possesses  of  adjusting  itself  to  vision  at  different  distances.     In  a 
normal  or  emmetropic  eye  parallel  rays  of  light  are  brought  to  a  focus  on 
16 


234  HUMAN    PHYSIOLOGY. 

the  retina  ;  but  divergent  rays — that  is,  rays  coming  from  a  near  luminous 
point — will  be  brought  to  a  focus  behind  the  retina,  provided  the  refractive 
media  remain  the  same  ;  as  a  result,  vision  would  be  indistinct,  from  the 
formation  of  diffusion  circles.  It  is  impossible  to  see  distinctly,  therefore, 
a  near  and  a  distant  object  at  the  same  time.  We  must  alternately  direct 
the  vision  from  one  to  the  other.  A  normal  eye  does  not  require  adjusting 
for  parallel  rays  ;  but  for  divergent  rays  a  change  in  the  eye  is  necessitated  ; 
this  is  termed  accommodation.  In  the  accommodation  for  near  vision  the 
lens  becomes  more  convex,  particularly  on  its  anterior  surface.  The  in- 
crease in  convexity  augments  its  refractive  power  ;  the  greater  the  degree 
of  divergence  of  the  rays  previous  to  entering  the  eye,  the  greater  the  in- 
crease of  convexity  of  the  lens  and  convergence  of  the  rays  after  passing 
through  it.  By  this  alteration  in  the  shape  of  the  lens  we  are  enabled  to 
focus  light  rays  coming  from,  and  to  see  distinctly,  near  as  well  as  distant 
objects. 

Function  of  the  Ciliary  Muscle. — Though  it  is  admitted  that  the 
change  in  the  convexity  of  the  lens  is  caused  by  the  contraction  of  the 
ciliary  muscle  and  the  relaxation  of  the  suspensory  ligament,  the  exact 
manner  in  which  it  does  so  is  not  understood.  When  the  eye  is  in  repose, 
as  in  distant  vision,  the  suspensory  ligament  is  tense,  and  the  lens  possesses 
that  degree  of  curvature  necessary  for  focusing  parallel  rays.  In  the  volun- 
tary efforts  to  accommodate  the  eye  for  near  vision,  the  ciliary  muscle  con- 
tracts, the  suspensory  ligament  relaxes,  and  the  lens,  inherently  elastic, 
bulges  forward  and  once  again  focuses  the  rays  upon  the  retina.  It  is? 
therefore,  termed  the  muscle  of  accommodation,  and  by  its  alternate  con- 
traction and  relaxation  the  lens  is  rendered  more  or  less  convex,  according 
to  the  requirements  for  near  and  distant  vision. 

Range  of  Accommodation. — Parallel  rays  coming  from  a  luminous 
point  distant  not  less  than  200  feet  do  not  require  adjustment ;  from  this 
point  up  to  infinity  no  accommodation  is  required  for  perfect  vision.  This 
is  termed  the  punctum  remoium,  and  indicates  the  distance  to  which  an 
object  may  be  removed  and  yet  distinctly  seen.  If  the  object  be  brought 
nearer  to  the  eye  than  200  feet,  the  accommodative  power  must  come  into 
play  ;  the  nearer  the  object,  the  more  energetic  must  be  the  contraction  of 
the  ciliary  muscle  and  the  consequent  increase  in  the  convexity  of  the  lens. 
At  a  distance  of  five  inches,  however,  the  power  of  accommodation  reaches 
its  maximum  ;  this  is  termed  the  punctum  proximum,  and  indicates  the 
nearest  point  at  which  an  object  may  be  seen  distinctly.  The  distance  be- 
tween these  two  points  is  the  range  of  accommodation. 


THE   SENSE   OF   SIGHT.  235 

Optic  Defects. — Astigmatism  is  a  condition  of  the  eye  which  prevents 
vertical  and  horizontal  lines  from  being  focused  at  the  same  time,  and  is 
due  to  a  greater  curvature  of  the  cornea  in  one  meridian  than  in  another. 

Spheric  aberration  is  a  condition  in  which  there  is  an  indistinctness  of 
an  image  from  the  unequal  refraction  of  the  rays  of  light  passing  through 
the  circumference  and  the  center  of  the  lens  ;  it  is  corrected  mainly  by  the 
iris,  which  cuts  off  the  marginal  rays,  and  transmits  only  those  passing 
through  the  center. 

Chromatic  aberration  is  a  condition  in  which  the  image  is  surrounded  by 
a  colored  margin,  from  the  decomposition  of  the  rays  of  light  into  their 
elementary  parts. 

Myopia,  or  shortsightness,  is  caused  by  an  abnormal  increase  in  the 
anteroposterior  diameter  of  the  eyeball,  or  by  a  hypernormal  refracting 
power  of  the  lens.  It  is  generally  due  to  the  first  cause  ;  the  lens,  being 
too  far  removed  from  the  retina,  forms  the  image  in  front  of  it,  and  the 
perception  becomes  dim  and  blurred.  Concave  glasses  correct  this  defect 
by  preventing  the  rays  from  converging  too  soon. 

Hypermetropia,  or  longsightness,  is  caused  by  a  shortening  of  the 
anteroposterior  diameter  or  by  a  subnormal  refractive  power  of  the  lens  ; 
the  focus  of  the  rays  of  light  would,  therefore,  be  behind  the  retina.  Con- 
vex glasses  correct  this  defect  by  converging  the  rays  of  light  more 
anteriorly. 

Presbyopia  is  a  loss  of  the  power  of  accommodation  of  the  eye  to  near 
objects,  and  usually  occurs  between  the  ages  of  forty  and  sixty  ;  it  is  reme- 
died by  the  use  of  convex  glasses. 

The  Iris. — The  iris  plays  the  part  of  a  diaphragm,  and  by  means  of  its 
central  aperture  the  pupil  regulates  the  quantity  of  light  entering  the 
interior  of  the  eye  ;  by  preventing  rays  from  passing  through  the  margin 
of  the  lens  it  diminishes  spheric  aberration.  The  size  of  the  pupil  depends 
upon  the  relative  degree  of  contraction  of  the  circular  and  radiating  fibers  ; 
the  variations  in  size  of  the  pupil  from  variations  in  the  degree  of  contrac- 
tion depend  upon  different  intensities  of  light.  If  the  light  be  intense,  the 
circular  fibers  contract,  and  diminish  the  size  of  the  pupil  ;  if  the  light 
diminishes  in  intensity,  the  circular  fibers  relax  and  the  pupil  enlarges. 

Point  of  Most  Distinct  Vision. — While  all  portions  of  the  retina  are 
sensitive  to  light,  their  sensibility  varies  within  wide  limits.  At  the 
macula  lutea,  and  more  especially  in  its  most  central  depression,  the  fovea, 
where  the  retinal  elements  are  reduced  practically  to  the  layer  of  rods  and 


236  HUMAN  PHYSIOLOGY. 

cones,  the  sensibility  reaches  its  maximum.  It  is  at  this  point  that  the 
image  is  found  when  vision  is  most  distinct.  The  macula  and  fovea  are 
always  in  the  line  of  direct  vision.  From  the  macula  toward  the  periphery 
of  the  retina  there  is  a  gradual  diminution  in  sensibility,  and  a  correspond- 
ing decline  in  the  distinctness  of  vision.  In  those  portions  of  the  retina 
lying  outside  the  macula,  the  indistinctness  of  vision  depends  not  only  on 
diminished  sensibility,  but  also  upon  inaccurate  focusing  of  the  rays. 

Blind  Spot. — Although  the  optic  nerve  transmits  the  impulses  excited 
in  the  retina  by  the  ethereal  vibration,  the  nerve-fibers  themselves  are  in- 
sensitive to  light.  At  the  point  of  entrance  of  the  optic  nerve,  owing  to 
the  absence  of  the  rods  and  cones,  the  rays  of  light  make  no  impression. 
This  is  the  blind  spot.  As  this  spot  is  not  in  the  line  of  vision,  no  dark 
point  is  ordinarily  observed  in  the  field  of  vision — the  circular  space  before 
a  fixed  eye  within  which  reflections  of  objects  are  perceptible. 

The  rods  and  cones  are  the  most  sensitive  portions  of  the  retina.  A  ray 
of  light  entering  the  eye  passes  entirely  through  the  various  layers  of  the 
retina,  and  is  arrested  only  upon  reaching  the  pigmentary  epithelium  in 
which  the  rods  and  cones  are  embedded.  As  to  the  manner  in  which  the 
objective  stimuli — light  and  color,  so  called — are  transformed  into  nerve 
impulses,  but  little  is  known.  It  is  probable  that  the  ethereal  vibrations 
are  transformed  into  heat,  which  excites  the  rods  and  cones.  These,  act- 
ing as  highly  specialized  end  organs  of  the  optic  nerve,  start  the  impulses 
on  their  way  to  the  brain,  where  the  seeing  process  takes  place.  As  to  the 
relative  function  of  the  rods  and  cones,  it  has  been  suggested,  from  the 
study  of  the  facts  of  comparative  anatomy,  that  the  rods  are  impressed  only 
by  differences  in  the  intensity  of  light,  while  the  cones,  in  addition,  are 
impressed  by  qualitative  differences  or  color. 

Accessory  Structures. — The  muscles  which  move  the  eyeball  are  six 
in  number — the  superior  and  inferior  recti,  the  external  and  internal  recti, 
the  superior  and  inferior  oblique  muscles.  The  four  recti  muscles,  arising 
from  the  apex  of  the  orbit,  pass  forward  and  are  inserted  into  the  sides  of 
the  sclerotic  coat ;  the  superior  and  inferior  muscles  rotate  the  eye  around 
a  horizontal  axis ;  the  external  and  internal  rotate  it  around  a  vertical 
axis. 

The  superior  oblique  muscle,  having  the  same  origin,  passes  forward  to 
the  inner  and  upper  angle  of  the  orbital  cavity,  where  its  tendon  passes 
through  a  cartilaginous  pulley ;  it  is  then  reflected  backward  and  inserted 
into  the  sclerotic  just  behind  the  transverse  diameter.     Its  function  is  to 


THE   SENSE   OF   HEARING.  237 

rotate  the  eyeball  in  such  a  manner  as  to  direct  the  pupil  dowmvard  and 
outward. 

The  inferior  oblique  muscle  arises  at  the  inner  angle  of  the  orbit,  and 
then  passes  outward  and  backward,  to  be  inserted  into  the  sclerotic.  Its 
function  is  to  rotate  the  eyeball  and  to  direct  the  pupil  upward  and  out- 
ward. 

By  the  associated  action  of  all  these  muscles,  the  eyeball  is  capable  of 
performing  all  the  varied  and  complex  movements  necessary  for  distinct 
vision. 

The  eyelids,  bordered  with  short,  stiff  hairs,  shade  the  eye  and  protect  it 
from  injury.  On  the  posterior  surface,  just  beneath  the  conjunctiva,  are 
the  Meibomian  glands,  which  secrete  an  oily  fluid  ;  this  covers  the  edge  of 
the  lids,  and  prevents  the  tears  from  flowing  over  the  cheek. 

The  lacrymal  glands  are  ovoid  in  shape,  and  are  situated  at  the  upper 
and  outer  part  of  the  orbital  cavity  ;  they  open  by  from  six  to  eight  ducts  at 
the  outer  portion  of  the  upper  lids. 

The  tears,  secreted  by  the  lacrymal  glands,  are  distributed  over  the  cor- 
nea by  the  lids  during  the  act  of  winking,  and  keep  it  moist  and  free  from 
dust.  The  excess  of  tears  passes  into  the  lacrymal  ducts,  which  begin  by 
two  minute  orifices,  one  on  each  lid,  at  the  inner  canthus.  They  conduct 
the  tears  into  the  nasal  duct,  and  so  into  the  nose. 


THE  SENSE  OF  HEARING. 

The  ear,  or  organ  of  hearing,  is  lodged  within  the  petrous  portion  of 
the  temporal  bone.  It  may  be,  for  convenience  of  description,  divided 
into  three  portions — viz  : 

1.  The  external  ear. 

2.  The  middle  ear. 

3.  The  internal  ear  or  labyrinth. 

The  external  ear  consists  of  the  pinna,  or  auricle,  and  the  external 
auditory  canal.  'Wit  pinna  consists  of  a  thin  layer  of  cartilage,  presenting 
a  series  of  elevations  and  depressions  ;  it  is  attached  by  fibrous  tissue  to  the 
outer  bony  edge  of  the  auditory  canal  ;  it  is  covered  by  a  layer  of  integu- 
ment continuous  with  that  covering  the  side  of  the  head.  The  general 
shape  of  the  pinna  is  concave,  and  presents,  %  little  below  the  center,  a  deep 
depression — the  concha.  The  external  aziditory  canal  extends  from  the 
concha  inward  for  a  distance  of  about  1%  inches.     It  is  directed  some- 


238  HUMAN    PHYSIOLOGY. 

what  forward  and  upward,  passing  over  a  convexity  of  bone,  and  then  dips 
downward  to  its  termination  ;  it  is  composed  of  both  bone  and  cartilage, 
and  is  lined  by  a  reflection  of  the  skin  covering  the  pinna.  At  the  external 
portion  of  the  canal  the  skin  contains  a  number  of  tubular  glands, — the 
ceruminous  glands, — which  in  their  conformation  resemble  the  perspiratory 
glands.     They  secrete  the  cerumen,  or  ear-wax. 

The  middle  ear,  or  tympanum,  is  an  irregularly  shaped  cavity  hol- 
lowed out  of  the  temporal  bone  and  situated  between  the  external  ear  and 
the  labyrinth.  It  is  narrow  from  side  to  side,  but  relatively  long  in  its 
vertical  and  anteroposterior  diameters ;  it  is  separated  from  the  external 
auditory  canal  by  a  membrane — the  membrana  tympani ;  from  the  internal 
ear  it  is  separated  by  an  osseomembranous  partition,  which  forms  a  common 
wall  for  both  cavities.  The  middle  ear  communicates  posteriorly  with  the 
mastoid  cells  ;  anteriorly  with  the  nasopharynx,  by  means  of  the  Eustachian 
tube.  The  interior  of  this  cavity  is  lined  by  mucous  membrane  continuous 
with  that  lining  the  pharynx. 

The  membrana  tympani  is  a  thin,  translucent,  nearly  circular  membrane, 
measuring  about  ■§  of  an  inch  in  diameter,  placed  at  the  inner  termination 
of  the  external  auditory  canal.  The  membrane  is  inclosed  within  a  ring 
of  bone,  which  in  the  fetal  condition  can  be  easily  removed,  but  in  the 
adult  condition  becomes  consolidated  with  the  surrounding  bone.  The 
membrana  tympani  consists  primarily  of  a  layer  of  fibrous  tissue,  arranged 
both  circularly  and  radially,  and  forms  the  membrana  propria  ;  externally 
it  is  covered  by  a  thin  layer  of  skin  continuous  with  that  lining  the  auditory 
canal ;  internally  it  is  covered  by  a  thin  mucous  membrane.  The  tympanic 
membrane  is  placed  obliquely  at  the  bottom  of  the  auditory  canal,  inclining 
at  an  angle  of  forty-five  degrees,  being  directed  from  behind  and  above 
downward  and  inward.  On  its  external  surface  this  membrane  presents 
a  funnel-shaped  depression,  the  sides  of  which  are  somewhat  convex. 

The  Ear  Bones. — Running  across  the  tympanic  cavity  and  forming  an 
irregular  line  of  joined  levers  is  a  chain  of  bones  which  articulate  with 
one  another  at  their  extremities.  They  are  known  as  the  malleus,  incus, 
and  stapes. 

The  form  and  position  of  these  bones  are  shown  in  figure  34. 

The  malleus  consists  of  a  head,  neck,  and  handle,  of  which  the  latter  is 
attached  to  the  inner  surface  of  the  membrana  tympani ;  the  incus,  or  anvil 
bone  presents  a  concave,  articular  surface,  which  receives  the  head  of  the 
malleus  ;  the  stapes,  or  stirrup  bone,  articulates  externally  with  the  long 


THE   SENSE   OF    HEARING. 


239 


process  of  the  incus,  and  internally,  by  its  oval  base,  with  the  edges  of  the 
foramen  ovale. 

The  tensor  tympani  muscle  consists  of  a  fleshy,  tapering  portion,  % 
of  an  inch  in  length,  which  terminates  in  a  slender  tendon  ;  it  arises  from 
the  cartilaginous  portion  of  the  Eustachian  tube  and  the  adjacent  surface  of 
the  sphenoid  bone.     From  this  origin  the  muscle  passes  nearly  horizontally 


Fig.  34. — Tympanum  and  Auditory  Ossicles  (Left)  Magnified. 
A.G.  External  meatus.  M.  Membrana  tympani,  which  is  attached  to  the  handle  of  the 
malleus,  n,  and  near  it  the  short  process,  p.  h.  Head  of  the  malleus,  a.  Incus; 
K,  its  short  process,  with  its  ligament;  1,  long  process,  s.  Sylvian  ossicle.  S. 
Stapes.  Ax,  Ax,  is  the  axis  of  rotation  of  the  ossicles ;  it  is  shown  in  perspective, 
and  must  be  imagined  to  penetrate  the  plane  of  the  paper,  t.  Line  of  traction  of  the 
tensor  tympani.  The  other  arrows  indicate  the  movement  of  the  ossicles  when  the 
tensor  contracts. 


backward  to  the  tympanic  cavity  ;  just  opposite  to  the"  fenestra  ovalis  its 
tendon  bends  at  a  right  angle  over  the  processus  cochleariformis,  and  then 
passes  outward  across  the  cavity,  to  be  inserted  into  the  angle  of  the  mal- 
leus near  the  neck. 

The  stapedius  muscle  emerges  from  the  cavity  of  a  pyramid  of  bone 
projecting  from  the  posterior  wall  of  the  tympanum  ;    the  tendon  passes 


240  HUMAN   PHYSIOLOGY. 

forward,  and  is  inserted  into  the  neck  of  the  stapes  bone,  posteriorly,  near 
its  point  of  articulation  with  the  incus. 

The  laxator  tympani  muscle,  so  called,  is  now  generally  regarded  as 
being  ligamentous  in  nature,  and  not  muscular. 

The  Eustachian  tube,  by  means  of  which  a  free  communication  is 
established  between  the  middle  ear  and  the  pharynx,  is  partly  bony  and 
partly  cartilaginous  in  structure.  It  measures  about  l^£  inches  in  length  ; 
commencing  at  its  opening  into  the  nasopharynx,  it  passes  upward  and 
outward  to  the  spine  of  the  sphenoid  bone,  at  which  point  it  becomes  some- 
what contracted ;  the  tube  then  dilates  as  it  passes  backward  into  the 
middle-ear  cavity ;  it  is  lined  by  mucous  membrane,  which  is  continued 
into  the  middle  ear  and  mastoid  cells. 

The  function  of  the  ear,  as  a  whole,  is  the  reception  and  transmis- 
sion of  aerial  vibrations  to  the  terminal  organs  concealed  within  the  in- 
ternal ear,  and  which  are  connected  with  the  auditory  nerve-fibers.  The 
excitation  of  these  end  organs  caused  by  the  impact  of  the  vibrations 
arouses  in  the  auditory  nerve  impulses  which  are  then  transmitted  to  the 
brain,  where  the  hearing  process  takes  place.  In  order  to  appreciate  the 
functions  of  the  individual  parts  of  the  ear,  a  few  of  the  characteristics  of 
sound  waves  must  be  kept  in  mind. 

Sound  Waves. — All  sounds  are  caused  by  vibrations  in  the  atmosphere 
which  have  been  communicated  to  it  by  vibrating  elastic  bodies,  such  as 
membranes,  strings,  rods,  etc.  These  vibrating  bodies  produce  in  the  air 
a  to-and-fro  movement  of  its  particles,  resulting  in  a  series  of  alternate 
condensations  and  rarefactions,  which  are  propagated  in  all  directions.  A 
complete  oscillation  of  a  particle  of  air  forward  and  backward  constitutes  a 
sound  wave.  Musical  sounds  are  caused  by  a  succession  of  regular  waves, 
which  follow  one  another  with  a  certain  rapidity.  Noises  are  caused  by 
the  impact  of  a  series  of  irregular  waves. 

All  sound  waves  possess  intensity,  pitch,  and  quality.  The  intensity,  or 
loudness,  of  a  sound  depends  upon  the  amplitude  of  its  vibrations  or  the 
extent  of  its  excursion.  The  pitch  depends  upon  the  number  of  vibra- 
tions which  affect  the  auditory  nerve  in  a  second  of  time  ;  the  pitch  of  the 
note  C,  the  first  below  the  leger  line  of  the  musical  scale,  is  caused  by 
256  vibrations  a  second;  the  pitch  of  the  same  note  an  octave  higher  is 
caused  by  512  vibrations  a  second.  If  the  vibrations  are  too  few  a  second, 
they  fail  to  be  perceived  as  a  continuous  sound  ;  the  minimum  number 
of  vibrations  capable  of  producing  a  sound  has  been  fixed  at  sixteen  a 


THE  SENSE   OF    HEARING.  241 

second ;  the  highest  pitched  musical  note  capable  of  being  heard  has  been 
shown  to  be  due  to  38,000  vibrations  a  second.  In  the  ascent  of  the 
musical  scales  there  is,  therefore,  a  gradual  increase  in  the  number  of 
vibrations  and  a  gradual  increase  in  the  pitch  of  the  sounds.  Between  the 
two  extreme  limits  lies  the  range  of  audibility,  which  embraces  eleven 
octaves,  of  which  seven  are  employed  in  the  musical  scale. 

The  quality  of  sound  depends  upon  a  combination  of  the  fundamental 
vibration  with  certain  secondary  vibrations  of  subdivisions  of  the  vibrating 
body.  These  so-called  over-tones  vary  in  intensity  and  pitch,  and  by 
modifying  the  form  of  the  primary  wave  produce  that  which  is  termed  the 
quality  of  sound. 

Function  of  the  Pinna  and  External  Auditory  Canal. — In  those 
animals  possessing  movable  ears  the  pinna  plays  an  important  part  in  the 
collection  of  sound  waves.  In  man,  in  whom  the  capability  of  moving  the 
pinna  has  been  lost,  it  is  doubtful  if  it  is  at  all  necessary  for  hearing. 
Nevertheless  an  individual  with  dull  hearing  may  have  the  perception  of 
sound  increased  by  placing  the  pinna  at  an  angle  of  45  degrees  to  the  side 
of  the  head.  The  external  auditory  canal  transmits  the  sonorous  vibra- 
tions to  the  tympanic  membrane.  Owing  to  the  obliquity  of  this  canal  it 
has  been  supposed  that  the  waves,  concentrated  at  the  concha,  undergo  a 
series  of  reflections  on  their  way  to  the  tympanic  membrane,  and,  owing  to 
the  position  of  this  membrane,  strike  it  almost  perpendicularly. 

Function  of  the  Tympanic  Membrane. — The  function  of  the  tym- 
panic membrane  appears  to  be  the  reception  of  sound  vibrations  by  being 
thrown  by  them  into  reciprocal  vibrations  which  correspond  in  intensity  and 
amplitude.  That  this  membrane  actually  reproduces  all  vibrations  within 
the  range  of  audibility  has  been  experimentally  demonstrated.  The  mem- 
brane not  being  fixed,  so  far  as  its  tension  is  concerned,  does  not  possess  a 
fixed  fundamental  note,  like  a  stationary  fixed  membrane,  and  is,  therefore, 
just  as  well  adapted  for  the  reception  of  one  set  of  vibrations  as  for  another. 
This  is  made  possible  by  variations  in  its  tension  in  accordance  with  the 
pitch  of  the  sounds.  In  the  absence  of  all  sound  the  membrane  is  in  a 
condition  of  relaxation  ;  with  the  advent  of  sound  waves  possessing  a 
gradual  increase  of  pitch,  as  in  the  ascent  of  the  music  scale,  the  ten- 
sion of  the  tympanic  membrane  is  gradually  increased  until  its  maximum 
tension  is  reached  at  the  upper  limit  of  the  range  of  audibility.  By  this 
change  in  tension  certain  tones  become  perceptible  and  distinct,  while 
others  become  indistinct  and  inaudible. 

Function  of  the  Tensor  Tympani  Muscle.  — The  function  of  this 


242  HUMAN   PHYSIOLOGY. 

muscle  is,  as  its  name  indicates,  to  increase  the  tension  of  the  membrane  in 
accordance  with  the  pitch  of  the  sound  wave.  The  tension  of  this  muscle 
playing  over  the  processus  cochleariformis  and  attached  at  almost  a  right 
angle  to  the  handle  of  the  malleus  will,  when  the  muscle  contracts,  pull  the 
handle  inward,  increase  the  convexity  of  the  membrane,  and  at  the  same 
time  increase  its  tension ;  with  the  relaxation  of  this  muscle,  the  handle  of 
the  malleus  passes  outward  and  the  tension  is  diminished.  The  contrac- 
tions of  the  tensor  muscle  are  reflex  in  character  and  excited  by  nerve- 
impulses  reaching  it  through  the  small  petrosal  nerve  and  otic  ganglion. 
The  number  of  nerve  stimuli  passing  to  the  muscle  and  determining  the 
degree  of  contraction  will  depend  upon  the  pitch  of  the  sound  wave  and  the 
subsequent  excitation  of  the  auditory  nerve.  The  tensor  tympani  muscle 
may  be  regarded  as  an  accommodative  apparatus  by  which  the  tympanic 
membrane  is  so  adjusted  as  to  enable  it  to  receive  vibrations  of  varying  de- 
grees of  pitch. 

Function  of  the  Ossicles. — The  function  of  the  chain  of  bones  is  to 
transmit  the  sound  wave  across  the  tympanic  cavity  to  the  internal  ear. 
The  first  of  these  bones,  the  malleus,  being  attached  to  the  tympanic  mem- 
brane, will  take  up  the  vibrations  much  more  readily  than  if  no  membrane 
intervened.  Owing  to  the  character  of  the  articulations,  when  the  handle 
of  the  malleus  is  drawn  inward,  the  position  of  the  bones  is  so  changed 
that  they  form  practically  a  solid  rod,  and  are  therefore  much  better  adapted 
for  the  transmission  of  molecular  vibrations  than  if  the  articulations  re- 
mained loose.  As  the  stapes  bone  is  somewhat  shorter  than  the  malleus, 
its  vibrations  are  slighter  than  those  of  the  tympanic  membrane,  and  by  this 
arrangement  the  amplitude  of  the  vibrations  is  diminished,  but  their  force 
increased. 

The  function  of  the  stapedius  muscle  is,  according  to  Henle,  to  fix 
the  stapes  bone  so  as  to  prevent  too  great  a  movement  from  being  commu- 
nicated to  it  from  the  incus  and  transmitted  to  the  perilymph.  It  may  be 
looked  upon,  therefore,  as  a  protective  muscle. 

The  function  of  the  Eustachian  tube  is  to  maintain  a  free  communi- 
cation between  the  cavity  of  the  middle  ear  and  the  nasopharynx.  The  pres- 
sure of  air  within  and  without  the  ear  is  thus  equalized,  and  the  vibrations 
of  the  tympanic  membrane  are  permitted  to  attain  their  maximum,  one  of 
the  conditions  essential  for  the  reception  of  sound  waves.  The  impairment 
in  the  acuteness  of  hearing  which  is  caused  by  an  unequal  pressure  of  the 
air  in  the  middle  ear  can  be  shown — 


THE   SENSE   OF   HEARING.  243 

1.  By  closing  the  mouth  and  nose  and  forcing  air  from  the  lungs  through 
the  Eustachian  tube  into  the  ear,  producing  an  increase  in  pressure. 

2.  By  closing  the  nose  and  mouth,  and  making  efforts  at  deglutition,  which 
withdraws  the  air  from  the  ear  and  diminishes  its  pressure. 

In  both  instances  the  free  vibrations  of  the  tympanic  membrane  are  in- 
terfered with.  The  pharyngeal  orifice  of  the  Eustachian  tube  is  opened 
by  the  action  of  certain  of  the  muscles  of  deglutition — viz.,  the  levator 
palati,  the  tensor  palati,  and  the  palato-pharyngei  muscles. 

The  internal  ear,  or  labyrinth,  is  located  in  the  petrous  portion  of  the 
temporal  bone,  and  consists  of  an  osseous  and  a  membranous  portion. 

The  osseous  labyrinth  is  divisible  into  three  parts — viz.,  the  vestibule, 
the  semicircular  canals,  and  the  cochlea. 

The  vestibule  is  a  small,  triangular  cavity,  which  communicates  with  the 
middle  ear  by  the  foramen  ovule  ;  in  the  natural  condition  it  is  closed  by 
the  base  of  the  stapes  bone.  The  filaments  of  the  auditory  nerve  enter  the 
vestibule  through  small  foramina  in  the  inner  wall,  at  the  fovea  hemi- 
spherica. 

The  semicircular  canals  are  three  in  number,  the  superior  vertical,  the 
inferior  vertical,  and  the  horizontal,  each  of  which  opens  into  the  cavity  of 
the  vestibule  by  two  openings,  with  the  exception  of  the  two  vertical,  which 
at  one  extremity  open  by  a  common  orifice. 

The  cochlea  forms  the  anterior  part  of  the  internal  ear.  It  is  a  gradually 
tapering  canal,  about  \)/2  inches  in  length,  which  winds  spirally  around  a 
central  axis,  the  modiolus,  two  and  one  half  times.  The  interior  of  the  coch- 
lea is  partly  divided  into  two  passages  by  a  thin  plate  of  bone,  the  lamina 
osseous  spiralis,  which  projects  from  the  central  axis  two  thirds  of  the  way 
across  the  canal.  These  passages  are  termed  the  scala  vestibuli  and  the  srala 
tympani,  from  their  communication  with  the  vestibule  and  tympanum.  The 
scala  tympani  communicates  with  the  middle  ear  through  the  foramen 
rotundum,  which,  in  the  natural  condition,  is  closed  by  the  second  mem- 
bran  a  tympani ;  superiorly  they  are  united  by  an  opening,  the  helicotrema. 

The  whole  interior  of  the  labyrinth,  the  vestibule,  the  semicircular  canals, 
and  the  scala  of  the  cochlea,  contains  a  clear,  limpid  fluid,  the  perilymph 
secreted  by  the  periosteum  lining  the  osseous  walls. 

The  membranous  labyrinth  corresponds  to  the  osseous  labyrinth  with 
respect  to  form,  though  it  is  somewhat  smaller  in  size. 

The  vestibular  portion  consists  of  two  small  sacs,  the  utricle  and 
the  saccule. 


244  HUMAN    PHYSIOLOGY. 

The  semicircular  canals  communicate  with  the  utricle  in  the  same  man- 
ner as  the  bony  canals  communicate  with  the  vestibule.  The  saccule  com- 
municates with  the  membranous  cochlea  by  the  canalis  reuniens.  In  the 
interior  of  the  utricle  and  saccule,  at  the  entrance  of  the  auditory  nerve, 
are  small  masses  of  carbonate  of  lime  crystals,  constituting  the  otoliths. 
Their  function  is  unknown. 

The  membranous  cochlea  is  a  closed  tube,  commencing  by  a  blind  ex- 
tremity at  the  first  turn  of  the  cochlea,  and  terminating  at  its  apex  by  a 
blind  extremity  also.  It  is  situated  between  the  edge  of  the  osseous  lamina 
spiralis  and  the  outer  wall  of  the  bony  cochlea,  and  follows  it  in  its  turns 
around  the  modiolus. 

A  transverse  section  of  the  cochlea  shows  that  it  is  divided  into  two 
portions  by  the  osseous  lamina  and  the  basilar  membrane  : 

1.  The  scala  vestibuli,  bounded  by  the  periosteum  and  membrane  of 
Reissner. 

2.  The  scala  tympani,  occupying  the  inferior  portion,  and  bounded  above 
by  the  septum,  composed  of  the  osseous  lamina  and  the  membrana 
basilaris. 

The  true  membranous  canal  is  situated  between  the  membrane  of  Reiss- 
ner and  the  basilar  membrane.  It  is  triangular  in  shape,  but  is  partly 
divided  into  a  triangular  portion  and  a  quadrilateral  portion  by  the  tectorial 
membrane. 

The  organ  of  Corti  is  situated  in  the  quadrilateral  portion  of  the  canal, 
and  consists  of  pillars  of  rods  of  the  consistence  of  cartilage.  They  are 
arranged  in  two  rows — the  one  internal,  the  other  external  ;  these  rods  rest 
upon  the  basilar  membrane  ;  their  bases  are  separated  from  one  another, 
but  their  upper  extremities  are  united,  forming  an  arcade.  In  the  internal 
row  it  is  estimated  there  are  about  3,500  and  in  the  external  row  about  5j2°° 
of  these  rods. 

On  the  inner  side  of  the  internal  row  is  a  single  layer  of  elongated  hair- 
cells  ;  on  the  outer  surface  of  the  external  row  are  three  such  layers  of  hair- 
cells.     Nothing  definite  is  known  as  to  their  function. 

The  endolymph  occupies  the  interior  of  the  utricle,  saccule,  and  mem- 
branous canals,  and  bathes  the  structures  in  the  interior  of  the  membranous 
cochlea  throughout  its  entire  extent. 

The   auditory  nerve  at  the  bottom  of    the  internal  auditory  meatus 

divides  into — 

I.  A  vestibular  branch,  which  is  distributed  to  the  utricle  and  to  the  semi- 
circular canals. 


VOICE  AND   SPEECH.  245 

2.  A  cochlear  branch,  which  passes  into  the  central  axis  at  its  base  and 
ascends  to  its  apex  ;  as  it  ascends,  fibers  are  given  off,  which  pass  be- 
tween the  plates  of  the  osseous  lamina,  to  be  ultimately  connected  with 
the  organ  of  Corti. 

The  function  of  the  semicircular  canals  appears  to  be  to  assist  in  main- 
taining the  equilibrium  of  the  body  ;  destruction  of  the  vertical  canal  is  fol- 
lowed by  an  oscillation  of  the  head  upward  and  downward  ;  destruction  of 
the  horizontal  canal  is  followed  by  oscillations  from  left  to  right.  "When 
the  canals  are  injured  on  both  sides,  the  animal  loses  the  power  of  main- 
taining equilibrium  upon  making  muscular  movements. 

Function  of  the  Cochlea. — It  is  regarded  as  possessing  the  power  of  ap- 
preciating the  quality  of  pitch  and  the  shades  of  different  musical  tones. 
The  elements  of  the  organ  of  Corti  are  analogous,  in  some  respects,  to  a 
musical  instrument,  and  are  supposed,  by  Helmholtz,  to  be  tuned  so  as  to 
vibrate  in  unison  with  the  different  tones  conveyed  to  the  internal  ear. 

Summary. — The  waves  of  sound  are  gathered  together  by  the  pinna  and 
external  auditory  meatus,  and  conveyed  to  the  membrana  tympani.  This 
membrane,  made  tense  or  lax  by  the  action  of  the  tensor  tympani  and  laxa- 
tor  tympani  muscles,  is  enabled  to  receive  sound  waves  of  either  high  or 
low  pitch.  The  vibrations  are  conducted  across  the  middle  ear  by  a  chain 
of  bones  to  the  foramen  ovale,  and  by  the  column  of  air  of  the  tympanum 
to  the  foramen  rotundum,  which  is  closed  by  the  second  membrana  tym- 
pani, the  pressure  of  the  air  in  the  tympanum  being  regulated  by  the  Eu- 
stachian tube. 

The  internal  ear  finally  receives  the  vibrations,  which  excite  vibrations 
successively  in  the  perilymph,  the  walls  of  the  membranous  labyrinth,  the 
endolymph,  and,  lastly,  the  terminal  filaments  of  the  auditory  nerve,  by 
which  they  are  conveyed  to  the  brain. 


VOICE  AND  SPEECH. 

The  larynx  is  the  organ  of  voice.  Speech  is  a  modification  of  voice,  and 
is  produced  by  the  teeth  and  the  muscles  of  the  lips  and  tongue,  coordi- 
nated in  their  action  by  stimuli  derived  from  the  cerebrum. 

The  structures  entering  into  the  formation  of  the  larynx  are  mainly  the 
thyroid,  cricoid,  and  arytenoid  cartilages  ;  they  are  so  situated  and  united 


246  HUMAN   PHYSIOLOGY. 

by  means  of  ligaments  and  muscles  as  to  form  a  firm  cartilaginous  box. 
The  larynx  is  covered  externally  by  fibrous  tissue,  and  lined  internally  with 
mucous  membrane. 

The  vocal  cords  are  four  ligamentous  bands,  running  anteroposteriorly 
across  the  upper  portion  of  the  larynx,  and  are  divided  into  the  two  superior 
or  false  vocal  cords,  and  the  two  inferior  or  true  vocal  cords  ;  they  are 
attached  anteriorly  to  the  receding  angle  of  the  thyroid  cartilages,  and  pos- 
teriorly to  the  anterior  part  of  the  base  of  the  arytenoid  cartilages.  The 
space  between  the  true  vocal  cords  is  the  rima  glottidis. 

The  muscles  which  have  a  direct  action  upon  the  movements  of  the 
vocal  cords  are  nine  in  number,  and  take  their  names  from  their  points  of 
origin  and  insertion — viz.,  the  two  crico-thyroid,  two  thyro -arytenoid,  two 
posterior  crico-arytenoid,  two  lateral  crico- arytenoid,  and  one  arytenoid 
muscles. 

The  crico-thyroid  muscles,  by  their  contraction,  render  the  vocal  cords 
more  tense  by  drawing  down  the  anterior  portion  of  the  thyroid  cartilage 
and  approximating  it  to  the  cricoid,  and  at  the  same  time  tilting  the  poste- 
rior portion  of  the  cricoid  and  arytenoid  cartilages  backward. 

The  thyro-aryteitoid,  by  their  contraction,  relax  the  vocal  cords  by  draw- 
ing the  arytenoid  cartilage  forward  and  the  thyroid  backward. 

The  posterior  crico-arytenoid  muscles,  by  their  contraction,  rotate  the 
arytenoid  cartilages  outward  and  thus  separate  the  vocal  cords  and  enlarge 
the  aperture  of  the  glottis.  They  principally  aid  the  respiratory  move- 
ments during  inspiration. 

The  lateral  cj'ico-arytenoid  muscles  are  antagonistic  to  the  former,  and 
by  their  contraction  rotate  the  arytenoid  cartilages  so  as  to  approximate  the 
vocal  cords  and  constrict  the  glottis. 

The  arytenoid  muscle  assists  in  the  closure  of  the  aperture  of  the  glottis. 

The  inferior  laryngeal  nerve  animates  all  the  muscles  of  the  larynx,  with 
the  exception  of  the  cricothyroid. 

Movements  of  the  Vocal  Cords. — During  respiration  the  movements 
of  the  vocal  cords  differ  from  those  occurring  during  the  production  of  voice. 

At  each  inspiration  the  true  vocal  cords  are  widely  separated,  and  the 
aperture  of  the  glottis  is  enlarged  by  the  action  of  the  crico-arytenoid  mus- 
cles, which  rotate  outward  the  anterior  angle  of  the  base  of  the  arytenoid 
cartilages ;  at  each  expiration  the  larynx  becomes  passive ;  the  elasticity  of 
the  vocal  cords  returns  them  to  their  original  position,  and  the  air  is  forced 
out  by  the  elasticity  of  the  lungs  and  the  walls  of  the  thorax. 


VOICE   AND    SPEECH.  247 

Phonation. — As  soon  as  phonation  is  about  to  be  accomplished,  a  marked 
change  in  the  glottis  is  noticed  with  the  aid  of  the  laryngoscope.  The  true 
vocal  cords  suddenly  become  approximated  and  are  made  parallel,  giving 
to  the  glottis  the  appearance  of  a  narrow  slit,  the  edges  of  which  are  capa- 
ble of  vibrating  accurately  and  rapidly  ;  at  the  same  time  their  tension  is 
much  increased. 

With  the  vocal  cords  thus  prepared,  the  expiratory  muscles  force  the 
column  of  air  into  the  lungs  and  trachea  through  the  glottis,  throwing  the 
edges  of  the  cords  into  vibration. 

The  pitch  of  sounds  depends  upon  the  extent  to  which  the  vocal  cords 
are  made  tense  and  the  length  of  the  aperture  through  which  the  air  passes. 
In  the  production  of  sounds  of  a  high  pitch,  the  tension  of  the  vocal 
cords  becomes  very  marked  and  the  glottis  diminished  in  length.  When 
sounds  having  a  low  pitch  are  emitted  from  the  larynx,  the  vocal  cords  are 
less  tense  and  their  vibrations  are  large  and  loose. 

The  quality  of  voice  depends  upon  the  length,  size,  and  thickness  of  the 
cords,  and  upon  the  size,  form,  and  construction  of  the  trachea,  the  larynx, 
and  the  resonant  cavities  of  the  pharynx,  nose,  and  mouth. 

The  compass  of  the  voice  comprehends  from  two  to  three  octaves.  The 
range  is  different  in  the  two  sexes,  the  lowest  note  of  the  male  being  about 
one  octave  lower  than  the  lowest  note  of  the  female  ;  while  the  highest 
note  of  the  male  is  an  octave  less  than  the  highest  note  of  the  female. 

The  varieties  of  voice — e.  g.,  bass,  baritone,  tenor,  contralto,  mezzo- 
soprano,  and  soprano — are  due  to  the  length  of  the  vocal  cords,  being 
longer  when  the  voice  has  a  low  pitch,  and  shorter  when  it  has  a  high 
pitch. 

Speech  is  the  faculty  of  expressing  ideas  by  means  of  combinations  of 
sounds,  in  obedience  to  the  dictates  ot  the  cerebrum. 

Articulate  saunds  may  be  divided  into  vowels  and  consonants.  The  vowe 
sounds,  a,  e,  i,  o,  u,  are  produced  in  the  larynx  by  the  vocal  cords.  The 
consonant  sounds  are  produced  in  the  air-passages  above  the  larynx  by  an 
interruption  of  the  current  of  air  by  the  lips,  tongue,  and  teeth  ;  the  conso- 
nants may  be  divided  into  : 

1.  Mutes,  b,  d,  k,p,  t,'c,g. 

2.  Dentals,  d,J,  s,  t,  z. 

3.  Nasals,  m,  n,  ng. 

4.  Labials,  b,p,f,  v,  m. 

5.  Gutturals,  k,  g,  c,  and  g  hard 

6.  Liquids,  /,  m,  n,  r. 


EMBRYOLOGY. 

Reproduction  is  the  function  by  which  the  species  is  preserved ;  it  is 
accomplished  by  the  organs  of  generation  in  the  two  sexes.  Embryology 
is  the  science  which  investigates  the  successive  stages  in  the  development 
of  the  embryo. 


GENERATIVE  ORGANS  OF  THE  FEMALE. 

The  generative  organs  of  the  female  consist  of  the  ovaries,  Fallo- 
pian tubes,  uterus,  and  vagina. 

The  ovaries  are  two  small,  ovoid,  flattened  bodies,  measuring  \yz  inches 
in  length  and  ^f  of  an  inch  in  width  ;  they  are  situated  in  the  cavity  of  the 
pelvis,  and  are  imbedded  in  the  posterior  layer  of  the  broad  ligament ;  at- 
tached to  the  uterus  by  a  round  ligament,  and  to  the  extremities  of  the  Fal- 
lopian tubes  by  the  fimbriae.  The  ovary  consists  of  an  external  membrane 
o  fibrous  tissue,  the  cortical  portion,  in  which  are  embedded  the  Graafian 
vesicles,  and  an  internal  portion,  the  stroma,  containing  blood-vessels. 

The  Graafian  vesicles  are  exceedingly  numerous,  but  are  situated  only 
in  the  cortical  portion.  Although  the  ovary  contains  the  vesicles  from  the 
period  of  birth,  it  is  only  at  puberty  that  they  attain  their  full  development. 
From  this  time  onward  to  the  catamenial  period  there  is  a  constant  growth 
and  maturation  of  the  Graafian  vesicles.  They  consist  of  an  external  in- 
vestment, composed  of  fibrous  tissues  and  blood-vessels,  in  the  interior  of 
which  is  a  layer  of  cells  forming  the  membrana  granulosa  ;  at  its  lower 
portion  there  is  an  accumulation  of  cells,  the  proligerous  disc,  in  which  the 
ovum  is  contained.  The  cavity  of  the  vesicle  contains  a  slightly  yellowish 
alkaline,  albuminous  fluid. 

The  ovum  is  a  globular  body,  measuring  about  T|^  of  an  inch  in 
diameter  :  it  consists  of  an  external  investing  membrane,  the  vitelline  mem- 
brane ;  a  central  granular  substance,  the  vitellus,  or  yolk ;  a  nucleus,  the 
germinal  vesicle,  in  the  interior  of  which  is  imbedded  the  nucleolus,  or 
germinal  spot. 

The  Fallopian  tubes  are  about  four  inches  in  length,  and  extend  out- 
ward from  the  upper  angles  of  the  uterus,  between  the  folds  of  the  broad 

248 


EMBRYOLOGY.  249 

ligaments,  and  terminate  in  a  fringed  extremity  which  is  attached  by  one 
of  the  fringes  to  the  ovary.     They  consist  of  three  coats  : 

1.  The  external,  or  peritoneal. 

2.  Middle,  or  muscular,  the  fibers  of  which  are  arranged  in  a  circular  or 
longitudinal  direction. 

3.  Internal,  or  mucous,  covered  with  ciliated  epithelial  cells,  which  are 
always  waving  from  the  ovary  toward  the  uterus. 

The  uterus  is  pyriform  in  shape,  and  may  be  divided  into  a  body  and 
neck  ;  it  measures  about  three  inches  in  length  and  two  inches  in  breadth 
in  the  unimpregnated  state.  At  the  lower  extremity  of  the  neck  is  the  os 
externum  ;  at  the  junction  of  the  neck  with  the  body  is  a  constriction,  the 
os  internum.  The  cavity  of  the  uterus  is  triangular  in  shape,  the  walls  of 
the  triangle  being  almost  in  contact. 

The  walls  of  the  uterus  are  made  up  of  several  layers  of  non-striated 
muscle-fibers,  covered  externally  by  peritoneum,  and  lined  internally  by 
mucous  membrane,  containing  numerous  tubular  glands,  and  covered  by 
ciliated  epithelial  cells. 

The  vagina  is  a  membranous  canal,  from  five  to  six  inches  in  length, 
situated  between  the  rectum  and  bladder.  It  extends  obliquely  upward 
from  the  surface,  almost  to  the  brim  of  the  pelvis,  and  embraces  at  its  upper 
extremity  the  neck  of  the  uterus. 

Discharge  of  the  Ovum. — As  the  Graafian  vesicle  matures  it  increases 
in  size,  from  an  augmentation  of  its  liquid  contents,  and  approaches  the 
surface  of  the  ovary,  where  it  forms  a  projection,  measuring  from  % 
to  %  of  an  inch.  The  maturation  of  the  vesicle  occurs  periodically, 
about  every  twenty-eight  days,  and  is  attended  by  the  phenomena  of  men- 
struation. During  this  period  of  active  congestion  of  the  reproductive 
organs  the  Graafian  vesicle  ruptures,  the  ovum  and  liquid  contents  escape, 
and  are  caught  by  the  fimbriated  extremity  of  the  Fallopian  tube,  which 
has  adapted  itself  to  the  posterior  surface  of  the  ovary.  The  passage  of 
the  ovum  through  the  Fallopian  tube  into  the  uterus  occupies  from  ten  to 
fourteen  days,  and  is  accomplished  by  muscular  contraction  and  by  the 
action  of  the  ciliated  epithelium. 

Menstruation  is  a  periodic  discharge  of  blood  from  the  mucous  mem- 
brane of  the  uterus,  due  to  a  fatty  degeneration  of  the  small  blood-vessels. 
Under  the  pressure  of  an  increased  amount  of  blood  in  the  reproductive 
organs,  attending  the  process  of  ovulation,  the  blood-vessels  rupture,  and  a 
hemorrhage  takes  place  into  the  uterine  cavity  ;  thence  it  passes  into  the 
17 


250 


HUMAN   PHYSIOLOGY. 


vagina.     Menstruation  lasts  from  five  to  six  days,  and  the  amount  of  blood 
discharged  averages  about  five  ounces. 

Corpus  Luteum. — For  some  time  previous  to  the  rupture  of  a  Graafian 
vesicle  it  increases  in  size  and  becomes  vascular ;  its  walls  become  thick- 
ened from  the  deposition  of  a  reddish-yellow,  glutinous  substance,  a  prod- 
uct of  cell  growth  from  the  proper  coat  of  the  follicle  and  the  membrana 
granulosa.  After  the  ovum  escapes  there  is  usually  a  small  effusion  of 
blood  into  the  cavity  of  the  follicle,  which  soon  coagulates,  loses  its  color- 
ing-matter, and  acquires  the  characteristics  of  fibrin,  but  it  takes  no  part  in 
the  formation  of  the  corpus  luteum.  The  walls  of  the  follicle  become  con- 
voluted and  vascular,  and  undergo  hypertrophy,  until  they  occupy  the  whole 
of  the  follicular  cavity.  At  its  period  of  fullest  development  the  corpus 
luteum  measures  3^  of  an  inch  in  length  and  ]/?,  of  an  inch  in  depth.  In  a 
few  weeks  the  mass  loses  its  red  color  and  becomes  yellow,  constituting 
the  corpus  luteum,  or  yellow  body.  It  then  begins  to  retract  and  becomes 
pale  ;  and  at  the  end  of  two  months  nothing  remains  but  a  small  cicatrix 
upon  the  surface  of  the  ovary.  Such  are  the  changes  in  the  follicle  if  the 
ovum  has  not  been  impregnated. 

The  corpus  luteum,  after  impregnation  has  taken  place,  undergoes  a  much 
slower  development,  becomes  larger,  and  continues  during  the  entire  period 
of  gestation.  The  difference  between  the  corpus  luteum  of  the  unimpreg- 
nated  and  pregnant  condition  is  expressed  in  the  following  table  by  Dalton  : 

Corpus  Luteum  of  Menstruation.       Corpus  Luteum  of  Pregnancy. 


At  the  end  of 
three  weeks. 
One  month. 


Two  months. 


Four  months. 


Six  months. 


Nine  months. 


Three  quarters  of  an  inch  in  diameter ;  central  qlot  red- 
dish ;  convoluted  wall  pale. 


Smaller ;  convoluted 
wall  bright  yellow  ;  clot 
still  reddish. 

Reduced  to  the  condi- 
tion of  an  insignificant 
cicatrix. 


Absent 
able. 

Absent. 


Absent. 


or    unnotice- 


Larger ;  convoluted  wall 
bright  yellow  ;  clot  still  reddish. 

Seven  eighths  of  an  inch  in 
diameter ;  convoluted  wall 
bright  yellow ;  clot  perfectly 
decolorized. 

Seven  eighths  of  an  inch  in 
diameter;  clot  pale  and  fibrinous; 
convoluted  wall  dull  yellow. 

Still  as  large  as  at  the  end  of 
second  month  ;  clot  fibrinous  ; 
convoluted  wall  paler. 

Half  an  inch  in  diameter ;  cen- 
tral clot  converted  into  a  radiat- 
ing cicatrix  ;  external  wall  toler- 
ably thick  and  convoluted,  but 
without  any  bright  yellow  color. 


EMBRYOLOGY.  251 

GENERATIVE   ORGANS  OF  THE  MALE. 

The  generative  organs  of  the  male  consist  of  the  testicles,  vasa 
deferentia,  vesiculce  seminales,  and  penis. 

The  testicles,  the  essential  organs  of  reproduction  in  the  male,  are  two 
oblong  glands,  about  1]/,  inches  in  length,  compressed  from  side  to  side, 
and  situated  in  the  cavity  of  the  scrotum. 

The  proper  coat  of  the  testicle,  the  tunica  albuginea,  is  a  white,  fibrous 
structure,  about  ^  of  an  inch  in  thickness  ;  after  enveloping  the  testicle, 
it  is  reflected  into  its  interior  at  the  posterior  border,  and  forms  a  vertical 
process,  the  mediastinum  testis,  from  which  septa  are  given  off,  dividing 
the  testicle  into  lobules. 

The  substance  of  the  testicle  is  made  up  of  the  seminiferous  tubules,  which 
exist  to  the  number  of  840 ;  they  are  exceedingly  convoluted,  and  when 
unravelled  are  about  thirty  inches  in  length.  As  they  pass  toward  the  apices 
of  the  lobules,  they  become  less  convoluted,  and  terminate  in  from  twenty 
to  thirty  straight  ducts,  the  vasa  recta,  which  pass  upward  through  the 
mediastinum  and  constitute  the  rete  testis.  At  the  upper  part  of  the  medi- 
astinum the  lobules  unite  to  form  from  nine  to  thirty  small  ducts,  the  vasa 
efferentia,  which  become  convoluted  and  form  the  globus  major  of  the 
epididymis  ;  the  continuation  of  the  tubes  downward  behind  the  testicle 
and  a  second  convolution  constitutes  the  body  and  globus  niinor. 

The  seminal  tubule  consists  of  a  basement  membrane  lined  by  granular 
nucleated  epithelium. 

The  vas  deferens,  the  excretory  duct  of  the  testicle,  is  about  two  feet  in 
length,  and  may  be  traced  upward  from  the  epididymis  to  the  under  surface 
of  the  base  of  the  bladder,  where  it  unites  with  the  duct  of  the  vesicula 
seminalis  to  form  the  ejaculatory  duct. 

The  vesiculae  seminales  are  two  lobulated,  pyriform  bodies  about  two 
inches  in  length,  situated  on  the  inner  surface  of  the  bladder. 

They  have  an  external  fibrous  coat,  a  middle  muscular  coat,  and  an  in- 
ternal mucous  coat,  covered  by  epithelium,  which  secretes  a  mucous  fluid. 
The  vesiculae  seminales  serve  as  reservoirs,  in  which  the  seminal  fluid  is 
temporarily  stored  up. 

The  ejaculatory  duct,  about  ^  of  an  inch  in  length,  opens  into  the 
urethra,  and  is  formed  by  the  union  of  the  vasa  deferentia  and  the  ducts  of 
the  vesiculae  seminales. 

The  prostate  gland  surrounds  the  posterior  extremity  of  the  urethra, 


252  HUMAN   PHYSIOLOGY. 

and  opens  into  it  by  from  twenty  to  thirty  openings,  the  orifices  of  Xhz pros- 
tatic tubules.  The  gland  secretes  a  fluid  which  forms  part  of  the  semen  and 
assists  in  maintaining  the  vitality  of  the  spermatozoa. 

Semen  is  a  complex  fluid,  made  up  of  the  secretions  from  the  testicles, 
the  vesiculse  seminales,  the  prostatic  and  urethral  glands.  It  is  grayish- 
white  in  color,  mucilaginous  in  consistence,  of  a  characteristic  odor,  and 
somewhat  heavier  than  water.  From  half  a  dram  to  a  dram  is  ejaculated 
at  each  orgasm. 

The  spermatozoa  are  peculiar  anatomic  elements,  developed  within 
the  seminal  tubules,  and  possess  the  power  of  spontaneous  movement. 
The  spermatozoa  consist  of  a  conoid  head  and  a  long,  filamentous  tail, 
which  is  in  continuous  and  active  motion  ;  so  long  as  they  remain  in  the 
vas  deferens  they  are  cpiiescent,  but  when  free  to  move  in  the  fluid  of  the 
vesicula;  seminales,  they  become  very  active. 

Origin. — The  spermatozoa  appear  at  the  age  of  puberty,  and  are  then 
constantly  formed  until  an  advanced  age.  They  are  developed  from  the 
nuclei  of  large,  round  cells  contained  in  the  anterior  of  the  seminal  tubules, 
as  many  as  fifteen  to  twenty  developing  in  a  single  cell. 

When  the  spermatozoa  are  introduced  into  the  vagina,  they  pass  readily 
into  the  uterus  and  through  the  Fallopian  tubes  toward  the  ovaries,  where 
they  remain  and  retain  their  vitality  for  a  period  of  from  eight  to  ten  days. 

Fecundation  is  the  union  of  the  spermatozoa  with  the  ovum  during  its 
passage  toward  the  uterus,  and  usually  takes  place  in  the  Fallopian  tube, 
just  outside  of  the  womb.  After  floating  around  the  ovum  in  an  active 
manner,  they  penetrate  the  vitelline  membrane,  pass  into  the  interior  of  the 
vitellus,  where  they  lose  their  vitality,  and,  along  with  the  germinal  vesicle, 
entirely  disappear. 


DEVELOPMENT  OF  ACCESSORY  STRUCTURES. 

Segmentation  of  the  Vitellus. — After  the  disappearance  of  the  sper- 
matozoa and  the  germinal  vesicle  there  remains  a  transparent,  granular, 
albuminous  substance,  in  the  center  of  which  a  new  nucleus  soon  appears ; 
this  constitutes  the  parent  cells,  and  is  the  first  stage  in  the  development  of 
the  new  being. 

Following  this,  the  vitellus  undergoes  segmentation ;  a  constriction  ap- 
pears on  the  opposite  side  of  the  vitellus,  which  gradually  deepens,  until  the 
yolk  is  divided  into  two  segments,  each  of  which  has  a  distinct  nucleus  and 


EMBRYOLOGY.  253 

nucleolus  ;  these  two  segments  undergo  a  further  division  into  four,  the 
four  into  eight,  the  eight  into  others,  and  so  on,  until  the  entire  vitellus  is 
divided  into  a  great  number  of  cells,  each  of  which  contains  a  nucleus  and 
a  nucleolus. 

The  peripheral  cells  of  this  "mulberry  mass"  then  arrange  themselves 
so  as  to  form  a  membrane,  and,  as  they  are  subjected  to  mutual  pressure, 
assume  a  polyhedral  shape,  which  gives  to  the  membrane  a  mosaic  appear- 
ance. The  central  part  of  the  vitellus  becomes  filled  with  a  clear  fluid.  A 
second  membrane  shortly  appears  within  the  first,  and  the  two  together 
constitute  the  external  and  internal  blastodermic  membranes. 

Germinal  Area. — At  about  this  period  there  is  an  accumulation  of  cells 
at  a  certain  spot  upon  the  surface  of  the  blastodermic  membranes,  which 
marks  the  position  of  the  future  embryo.  This  spot,  at  first  circular,  soon 
becomes  elongated,  and  forms  the  primitive  trace,  around  which  is  a  clear 
space,  the  area  pellucida,  which  is  itself  surrounded  by  a  darker  region, 
the  area  opaca. 

The  primitive  trace  soon  disappears,  and  the  area  pellucida  becomes 
guitar-shaped  ;  a  new  groove,  the  medullary  groove,  is  now  formed,  which 
develops  from  before  backward,  and  becomes  the  neural  canal. 

Blastodermic  Membranes. — The  embryo,  at  this  period,  consists  of 
three  layers — viz.,  the  external  and  the  internal  blastodermic  membranes 
and  a  middle  membrane  formed  by  a  genesis  of  cells  from  their  internal 
surfaces.     These  layers  are  known  as  the  epiblast,  mesoblast,  and  hypoblast. 

The  epiblast  gives  rise  to  the  central  nervous  system,  the  epidermis  of  the 
skin  and  its  appendages,  and  the  primitive  kidneys. 

The  mesoblast  gives  rise  to  the  dermis,  muscles,  bones,  nerves,  blood- 
vessels, sympathetic  nervous  system,  connective  tissue,  the  urinary  and  re- 
productive apparatus,  and  the  walls  of  the  alimentary  canal. 

The  hypoblast  gives  rise  to  the  epithelial  lining  of  the  alimentary  canal 
and  its  glandular  appendages,  the  liver  and  pancreas,  and  the  epithelium 
of  the  respiratory  tract. 

Dorsal  Laminae. — As  development  advances,  the  true  medullary 
groove  deepens,  and  there  arise  two  longitudinal  elevations  of  the  epiblast, 
— the  dorsal  lamina,  one  on  either  side  of  the  groove, — which  grow  up, 
arch  over,  and  unite  so  as  to  form  a  closed  tube,  the  primitive  central 
nervous  system. 

The  chorda  dorsalis  is  a  cylindric  rod  running  almost  throughout  the 
entire  length  of  the  embryo.  It  is  formed  by  an  aggregation  of  mesoblastic 
cells,  and  is  situated  immediately  beneath  the  medullary  groove. 


254  HUMAN    PHYSIOLOGY. 

Primitive  Vertebrae. — On  either  side  of  the  neural  canal  the  cells  of 
the  mesoblast  undergo  a  longitudinal  thickening,  which  develops  and  ex- 
tends around  the  neural  canal  and  the  chorda  dorsalis,  and  forms  the  arches 
and  bodies  of  the  vertebrae.  They  become  divided  transversely  into  four- 
sided  segments. 

The  mesoblast  now  separates  into  two  layers  :  the  external,  joining  with 
the  epiblast,  forms  the  somatopleura  ;  the  internal,  joining  with  the  hypo- 
blast, forms  the  splanchnapleura  ;  the  space  between  them  constitutes  the 
pleuro-fieritoneal  cavity. 

Visceral  Laminae.  —  The  walls  of  the  pleuro-peritoneal  cavity  are 
formed  by  a  downward  prolongation  of  the  somatopleura  (the  visceral 
I  a  mince),  which,  as  they  extend  around  in  front,  pinch  off  a  portion  of  the 
yolk-sac  (formed  by  the  splanchnopleura),  which  becomes  the  primitive 
alimentary  canal ;  the  lower  portion,  remaining  outside  of  the  body  cavity, 
forms  the  umbilical  vesicle,  which  after  a  time  disappears. 

Formation  of  Fetal  Membranes. — The  amnion  appears  shortly  after 
the  embryo  begins  to  develop,  and  is  formed  by  folds  of  the  epiblast  and 
external  layer  of  the  mesoblast,  rising  up  in  front  and  behind  and  on  each 
side  ;  these  amniotic  folds  gradually  extend  over  the  back  of  the  embryo 
to  a  certain  point,  where  they  coalesce  and  inclose  a  cavity — the  amniotic 
cavity.  The  membranous  partition  between  the  folds  disappears,  and  the 
outer  layer  recedes  and  becomes  blended  with  the  vitelline  membrane,  con- 
stituting the  chorion — the  external  covering  of  the  embryo. 

The  Allantois. — As  the  amnion  develops,  there  grows  out  from  the 
posterior  portion  of  the  alimentary  canal  a  pouch,  or  diverticulum  (the 
allantois),  which  carries  blood-vessels  derived  from  the  intestinal  circula- 
tion. As  it  gradually  enlarges  it  becomes  more  vascular,  and  inserts  itself 
between  the  two  layers  of  the  amnion,  coming  into  intimate  contact  with 
the  external  layer.  Finally,  from  increased  growth,  it  completely  surrounds 
the  embryo,  and  its  edges  become  fused  together. 

In  the  bird  the  allantois  is  a  respiratory  organ,  absorbing  oxygen  and 
exhaling  carbonic  acid  ;  it  also  absorbs  nutritive  matter  from  the  interior  of 
the  egg. 

Amniotic  Fluid. — The  amnion,  when  first  formed,  is  in  close  contact 
with  the  surface  of  the  ovum ;  but  it  soon  enlarges,  and  becomes  filled 
with  a  clear,  transparent  fluid,  containing  albumin,  glucose,  fatty  matters, 
urea,  and  inorganic  salts.  It  increases  in  amount  up  to  the  latter  period 
of  gestation,  when  it  amounts  to  about  two  pints.     In  the  space  between 


EMBRYOLOGY.  255 

the  amnion  and  allantois  is  a  gelatinous  material,  which  is  encroached 
upon  and  finally  disappears  as  the  amnion  and  allantois  come  in  contact,  at 
about  the  fifth  month. 

The  chorion,  the  external  investment  of  the  embryo,  is  formed  by  a 
fusion  of  the  original  vitelline  membrane,  the  external  layer  of  the  amnion, 
and  the  allantois.  The  external  surface  now  becomes  covered  with  villous 
processes,  which  increase  in  number  and  size  by  the  continual  budding 
and  growth  of  club-shaped  processes  from  the  main  stem,  and  give  to  the 
chorion  a  shaggy  appearance.  They  consist  of  a  homogeneous  granular 
matter,  and  are  penetrated  by  branches  of  the  blood-vessels  derived  from 
the  aorta. 

The  presence  of  villous  processes  in  the  uterine  cavity  is  proof  positive 
of  the  previous  existence  of  a  fetus.  They  are  characteristic  of  the  chorion, 
and  are  found  under  no  other  circumstances. 

At  about  the  end  of  the  second  month  the  villosities  begin  to  atrophy 
and  disappear  from  the  surface  of  the  chorion,  with  the  exception  of  those 
situated  at  the  points  of  entrance  of  the  fetal  blood-vessels,  which  occupy 
about  one  third  of  its  surface,  where  they  continue  to  grow  longer,  become 
more  vascular,  and  ultimately  assist  in  the  formation  of  the  placenta  ;  the 
remaining  two  thirds  of  the  surface  loses  its  villi  and  blood-vessels  and 
becomes  a  simple  membrane. 

The  umbilical  cord  connects  the  fetus  with  that  portion  of  the  chorion 
which  forms  the  fetal  side  of  the  placenta.  It  is  a  process  of  the  allantois, 
and  contains  two  arteries  and  a  vein,  which  have  a  more  or  less  spiral 
direction.  It  appears  at  the  end  of  the  first  month,  and  gradually  increases 
in  length  until,  at  the  end  of  gestation,  it  measures  about  twenty  inches. 
The  cord  is  also  surrounded  by  a  process  of  the  amnion. 

Development  of  the  Decidual  Membrane.  —  The  interior  of  the 
uterus  is  lined  by  a  thin,  delicate  mucous  membrane,  in  which  are  embedded 
immense  numbers  of  tubules,  terminating  in  blind  extremities — the  uterine 
tubules.  At  each  period  of  menstruation  the  mucous  membrane  becomes 
thickened  and  vascular,  which  condition,  however,  disappears  after  the 
usual  menstrual  discharge.  When  the  ovum  becomes  fecundated,  the 
mucous  membrane  takes  on  an  increased  growth,  becomes  more  hypertro- 
phied  and  vascular,  sends  up  little  processes  or  elevations  from  its  surface, 
and  constitutes  the  decidtia  vera. 

As  the  ovum  passes  from  the  Fallopian  tube  into  the  interior  of  the 
uterus,  the  primitive  vitelline  membrane,  covered  with  villosities,  becomes 
entangled  with  the  processes  of  the  mucous  membrane.     A  portion  of  the 


256  HUMAN    PHYSIOLOGY. 

decidua  vera  then  grows  up  on  all  sides  and  incloses  the  ovum,  forming  the 
decidua  refiexa,  while  the  villous  processes  of  the  chorion  insert  themselves 
into  the  uterine  tubules  and  in  the  mucous  membrane  between  them. 

As  development  advances,  the  decidua  refiexa  increases  in  size,  and  at 
about  the  end  of  the  fourth  month  comes  in  contact  with  the  decidua  vera, 
with  which  it  is  ultimately  fused. 

The  Placenta. — Of  all  the  embryonic  structures,  the  placenta  is  the 
most  important.  It  is  formed  in  the  third  month,  and  then  increases  in 
size  until  the  seventh  month,  when  a  retrogressive  metamorphosis  takes 
place  until  its  separation  during  labor,  at  which  time  it  is  of  an  oval  or 
rounded  shape,  and  measures  from  seven  to  nine  inches  in  length,  six  to 
eight  inches  in  breadth,  and  weighs  from  fifteen  to  twenty  ounces.  It  is 
most  frequently  situated  at  the  upper  and  posterior  part  of  the  inner  surface 
of  the  uterus. 

The  placenta  consists  of  two  portions,  a  fetal  and  a  maternal. 

The  fetal  portion  is  formed  by  the  villi  of  the  chorion,  which,  by  devel- 
oping, rapidly  increase  in  size  and  number.  They  become  branched  and 
penetrate  the  uterine  tubules,  which  enlarge  and  receive  their  many  rami- 
fications. The  capillary  blood-vessels  in  the  anterior  of  the  villi  also 
enlarge  and  freely  anastomose  with  one  another. 

The  maternal  portion  is  formed  from  that  part  of  the  hypertrophied  and 
vascular  decidual  membrane  between  the  ovum  and  the  uterus,  the  decidua 
serotina.  As  the  placenta  increases  in  size,  the  maternal  blood-vessels 
around  the  tubules  become  more  and  more  numerous,  and  gradually  fuse 
together,  forming  great  lakes,  which  constitute  sinuses  in  the  walls  of  the 
uterus. 

As  the  terminal  period  of  gestation  approaches,  the  villi  extend  deeper 
into  the  decidua,  while  the  sinuses  in  the  maternal  portion  become  larger 
and  extend  further  into  the  chorion.  Finally,  from  excessive  development  of 
the  blood-vessels,  the  structures  between  them  disappear,  and  as  their  walls 
come  in  contact  they  fuse  together,  so  that,  ultimately,  the  maternal  and 
fetal  blood  are  separated  only  by  a  thin  layer  of  a  homogeneous  substance. 
When  fully  formed,  the  placenta  consists  principally  of  blood-vessels  inter- 
lacing in  every  direction.  The  blood  of  the  mother  passes  from  the  uterine 
vessels  into  the  lake  surrounding  the  villi ;  the  blood  from  the  fetus  flows 
from  the  umbilical  arteries  into  the  interior  of  the  villi ;  but  there  is  not  at 
any  time  an  intermingling  of  blood,  the  two  being  separated  by  a  delicate 
membrane  formed  by  a  fusion  of  the  walls  of  the  blood-vessels  and  the 
walls  of  the  villi  and  uterine  sinuses. 


EMBRYOLOGY.  257 

The  function  of  the  placenta,  besides  nutrition,  is  that  of  a  respiratory 
organ,  permitting  the  oxygen  of  the  maternal  blood  to  pass  by  osmosis 
through  the  delicate  placental  membrane  into  the  blood  of  the  fetus ;  at 
the  same  time  permitting  the  carbonic  acid  and  other  waste  products,  the 
result  of  nutritive  changes  in  the  fetus,  to  pass  into  the  maternal  blood,  and 
so  to  be  carried  to  the  various  eliminating  organs. 

Through  the  placenta  also  passes  all  the  nutritious  materials  of  the 
maternal  blood  which  are  essential  to  the  development  of  the  embryo. 

At  about  the  middle  of  gestation  there  develops  beneath  the  decidual 
membrane  a  new  mucous  membrane,  destined  to  perform  the  functions  of 
the  old  when  it  is  extruded  from  the  womb,  along  with  the  other  embryonic 
structures,  during  parturition. 


DEVELOPMENT  OF  THE  EMBRYO. 

Nervous  System. — The  cerebro-spinal  axis  is  formed  within  the 
medullary  canal  by  the  development  of  cells  from  its  inner  surfaces,  which, 
as  they  increase,  fill  up  the  canal,  and  there  remains  only  the  central  canal 
of  the  cord.  The  external  surface  gives  rise  to  the  dura  mater  and  pia 
mater.  The  neural  canal  thus  formed  is  a  tubular  membrane  ;  it  terminates 
posteriorly  in  an  oval  dilatation,  and  anteriorly  in  a  bulbous  extremity, 
which  soon  becomes  partially  contracted,  and  forms  the  anterior,  middle, 
and  posterior  cerebral  vesicles,  from  which  are  ultimately  developed  the  cere- 
brum, the  corpora  quadrigemina,  and  the  medulla  oblongata,  respectively. 

The  anterior  vesicle  soon  subdivides  into  two  secondary  vesicles,  the 
larger  of  which  becomes  the  hemispheres,  the  smaller  the  optic  thalami; 
the  posterior  vesicle  also  divides  into  two,  the  anterior  becoming  the  cere- 
bellum, the  posterior  the  pons  Varolii  and  medulla  oblongata. 

About  the  seventh  week  the  straight  chain  of  cerebral  vesicles  becomes 
curved  from  behind  forward  and  forms  three  prominent  angles.  As  devel- 
opment advances,  the  relative  size  of  the  encephalic  masses  changes.  The 
cerebrum,  developing  more  rapidly  than  the  posterior  portion  of  the  brain, 
soon  grows  backward  and  arches  over  the  optic  thalami  and  the  tubercula 
quadrigemina  ;  the  cerebellum  overlaps  the  medulla  oblongata. 

The  surface  of  the  cerebral  hemispheres  is  at  first  smooth,  but  at  about 
the  fourth  month  begins  to  be  marked  by  the  future  fissures  and  convolu- 
tions. 

The  eye  is  formed  by  a  little  bud  projecting  from  the  side  of  the  anterior 
vesicle.     It  is  at  first  hollow,  but  becomes  lined  with  nervous  matter,  form- 


258  HUMAN    PHYSIOLOGY. 

ing  the  optic  nerve  and  retina  ;  the  remainder  of  the  cavity  is  occupied  by 
the  vitreous  body.  The  anterior  portion  of  the  pouch  becomes  invaginated 
and  receives  the  crystalline  lens,  which  is  a  product  of  the  epiblast,  as  is 
also  the  cornea.  The  iris  appears  as  a  circular  membrane  without  a  cen- 
tral aperture,  about  the  seventh  week  ;  the  eyelids  are  formed  between  the 
second  and  third  months. 

The  internal  ear  is  developed  from  the  auditory  vesicle,  budding  from 
the  third  cerebral  vesicle  ;  the  membranous  vestibule  appears  first,  and 
from  it  diverticula  are  given  off,  which  become  the  semicircular  canals  and 
the  cochlea. 

The  cavity  of  the  tympanum,  the  Eustachian  tube,  and  the  external 
auditory  canal  are  the  remains  of  the  first  branchial  cleft,  the  cavity  of  this 
cleft  being  subdivided  into  the  tympanum  and  external  auditory  meatus  by 
the  membrana  tympani. 

The  Skeleton. — The  chorda  dorsalis,  the  primitive  part  of  the  vertebral 
column,  is  a  cartilaginous  rod  situated  beneath  the  medullary  groove.  It 
is  a  temporary  structure,  and  disappears  as  the  true  bony  vertebrae  develop. 
On  either  side  are  the  quadrate  masses  of  the  mesoblast,  the  primitive  ver- 
tebrae, which  send  processes  upward  and  around  the  medullary  groove,  and 
downward  and  around  the  chorda  dorsalis,  forming  in  these  situations  the 
arches  and  bodies  of  the  future  vertebrae. 

More  externally  the  outer  layers  of  the  mesoblast  and  epiblast  arch  down- 
ward and  forward,  forming  the  ventral  laminae,  in  which  develop  the 
muscles  and  bones  of  the  abdominal  walls. 

The  trtie  cranium  is  an  anterior  development  of  the  vertebral  column, 
and  consists  of  the  occipital,  parietal,  and  frontal  segments,  which  corre- 
spond to  the  three  cerebral  vesicles.  The  base  of  the  cranium  consists,  at 
this  period,  of  a  cartilaginous  rod  on  either  side  of  the  anterior  extremity 
of  the  chorda  dorsalis,  in  which  three  centers  of  ossification  appear,  the 
basi-occipital,  the  basisphenoid,  and  the  presphenoid.  They  ultimately 
develop  into  the  basilar  process  of  the  occipital  bone  and  the  body  of  the 
sphenoid. 

The  entire  skeleton  is  at  first  either  membranous  or  cartilaginous.  At 
the  beginning  of  the  second  month  centers  of  ossification  appear  in  the  jaws 
and  clavicle  ;  as  development  advances  the  ossific  points  in  all  the  future 
bones  extend,  until  ossification  is  completed. 

The  limbs  develop  from  four  little  buds  projecting  from  the  sides  of  the 
embryo,  which,  as  they  increase  in  length,  separate  into  the  thigh,  leg,  and 


EMBRYOLOGY.  259 

foot,  and  the  arm,  forearm,  and  hand  ;  the  extremities  of  the  limbs  undergo 
subdivision,  to  form  the  fingers  and  toes. 

Face  and  Visceral  Arches. — In  the  facial  and  cervical  regions  the 
visceral  laminae  send  up  three  processes,  the  visceral  arches,  separated  by 
clefts,  the  visceral  clefts. 

The  first,  or  the  mandibular  arches,  unite  in  the  median  line  to  form 
the  lower  jaw,  and  superiorly  form  the  malleus.  A  process  jutting  from 
its  base  grows  forward,  unites  with  the  frontonasal  process  growing  from 
above,  and  forms  the  upper  jaw.  When  the  superior  maxillary  processes 
fail  to  unite  there  results  the  cleft-palate  deformity  ;  if  the  integument  also 
fails  to  unite,  there  results  the  hare-lip  deformity.  The  space  above  the 
mandibular  arch  becomes  the  mouth. 

The  second  arch  develops  the  incus  and  stapes  bones,  the  styloid  process 
and  ligament,  and  the  lesser  cornu  of  the  hyoid  bone.  The  cleft  between 
the  first  and  second  arches  partially  closes  up,  but  there  remains  an  opening 
at  the  side,  which  becomes  the  Eustachian  tube,  tympanic  cavity,  and  ex- 
ternal auditory  meatus. 

The  third  arch  develops  the  body  and  greater  cornu  of  the  hyoid  bone. 

Alimentary  Canal  and  Its  Appendages. — The  alimentary  canal  is 
formed  by  a  pinching-off  of  the  yolk-sac  by  the  visceral  plates  as  they  grow 
downward  and  forward.  It  consists  of  three  distinct  portions — the  fore  gut, 
the  hind  gut,  and  the  central  part,  which  communicates  for  some  time  with 
the  yolk-sac.  It  is  at  first  a  straight  tube,  closed  at  both  extremities,  lying 
just  beneath  the  vertebral  column.  The  canal  gradually  increases  in  length 
and  becomes  more  or  less  convoluted  ;  at  its  anterior  portion  two  pouches 
appear,  which  become  the  cardiac  and  pyloric  extremities  of  the  stomach, 
At  about  the  seventh  week  the  inferior  extremity  of  the  intestine  is  brought 
into  communication  with  the  exterior  by  an  opening,  the  anus.  Anteriorly 
the  mouth  and  pharynx  are  formed  by  an  involution  of  epiblast,  which 
deepens  until  it  communicates  with  the  fore  gut. 

Th  liver  appears  as  a  slight  protrusion  from  the  sides  of  the  alimentary 
canal,  about  the  end  of  the  first  month  ;  it  grows  very  rapidly,  attains  a 
large  size,  and  almost  fills  up  the  abdominal  cavity.  The  hepatic  cells  are 
derived  from  the  intestinal  epithelium,  the  vessels  and  connective  tissue 
from  the  mesoblast. 

The  pancreas  is  formed  by  the  hypoblastic  membrane.  It  originates  in 
two  small  ducts  budding  from  the  duodenum,  which  divide  and  subdivide, 
and  develop  the  glandular  structure. 

The  lungs  are  developed  from  the  anterior  part  of  the  esophagus.     At 


260  HUMAN   PHYSIOLOGY. 

first  a  small  bud  appears,  which,  as  it  lengthens,  divides  into  two  branches  ; 
secondary  and  tertiary  processes  are  given  off  from  these,  which  form  the 
bronchial  tubes  and  air-cells.  The  lungs  originally  extended  into  the  ab- 
dominal cavity,  but  became  confined  to  the  thorax  by  the  development  of 
the  diaphragm. 

The  bladder  is  formed  by  a  dilatation  of  that  portion  of  the  allantois 
remaining  within  the  abdominal  cavity.  It  is  at  first  pear-shaped  and 
communicates  with  the  intestine,  but  later  becomes  separated  and  opens 
exteriorly  by  the  urethra.  It  is  attached  to  the  abdominal  walls  by  a 
rounded  cord — the  urachus,  the  remains  of  a  portion  of  the  allantois. 

Genito-urinary  Apparatus. — The  Wolffian  bodies  appear  about  the 
thirteenth  day,  as  long,  hollow  tubes  running  along  each  side  of  the  primi- 
tive vertebral  column.  They  are  temporary  structures,  and  are  sometimes 
called  the  primordial  kidneys.  The  Wolffian  bodies  consist  of  tubules 
which  run  transversely  and  are  lined  with  epithelium  ;  internally  they  be- 
come invaginated  to  receive  tufts  of  blood-vessels ;  externally  they  open 
into  a  common  excretory  duct,  the  dud  of  the  Wolffian  body,  which  unites 
with  the  duct  of  the  opposite  body  and  empties  into  the  intestinal  canal 
at  a  point  opposite  the  allantois.  On  the  outer  side  of  the  Wolffian  body 
there  appears  another  duct,  the  duct  of  Miiller,  which  also  opens  into  the 
intestine. 

Behind  the  Wolffian  bodies  are  developed  the  structures  which  become 
either  the  ovaries  or  testicles.  In  the  development  of  the  female  the 
Wolffian  bodies  and  their  ducts  disappear  ;  the  extremities  of  the  Mullerian 
ducts  dilate  and  form  the  fimbriated  extremity  of  the  Fallopian  tubes,  while 
the  lower  portions  coalesce  to  form  the  body  of  the  uterus  and  vagina, 
which  now  separate  themselves  from  the  intestine. 

In  the  development  of  the  male  the  Mullerian  ducts  atrophy,  and  the 
ducts  of  the  Wolffian  body  ultimately  form  the  epididymis  and  vas  defer- 
ens. About  the  seventh  month  the  testicles  begin  to  descend,  and  by  the 
ninth  month  have  passed  through  the  abdominal  ring  into  the  scrotum. 

The  kidneys  are  developed  out  of  the  Wolffian  bodies.  They  consist  of 
little  pyramidal  lobules,  composed  of  tubules  which  open  at  the  apex  into 
the  pelvis.  As  they  pass  outward  they  become  convoluted  and  cup-shaped 
at  their  extremities,  receive  a  tuft  of  blood-vessels,  and  form  the  Malpig- 
hian  bodies. 

The  ureters  are  developed  from  the  kidneys  and  pass  downward  to  be 
connected  with  the  bladder. 

The  circulatory  apparatus  assumes  three  forms  at  different  periods  of 


EMBRYOLOGY.  261 

life,  all  having  reference   to  the  manner  in  which  the  embryo  receives 
nutritive  matter  and  is  freed  of  waste  products. 

The  vitelline  circulation  appears  first  and  absorbs  nutritive  material 
from  the  vitellus.  It  is  formed  by  blood-vessels  which  emerge  from  the 
body  and  ramify  over  a  portion  of  the  vitelline  membrane,  constituting  the 
area  vasculosa.  The  heart,  lying  in  the  median  line,  gives  off  two  arches, 
which  unite  to  form  the  abdominal  aorta,  from  which  two  large  arteries 
are  given  off,  passing  into  the  vascular  area  ;  the  venous  blood  is  returned 
by  veins  which  enter  the  heart.  These  vessels  are  known  as  the  omphalo- 
mesenteric arteries  and  veins.  The  vitelline  circulation  is  of  short  dura- 
tion in  mammals,  as  the  supply  of  nutritive  matter  in  the  vitellus  soon  be- 
comes exhausted. 

The  placental  circulation  becomes  established  when  the  blood-vessels  in 
the  allantois  enter  the  villous  processes  of  the  chorion  and  come  into  close 
relationship  with  the  maternal  blood-vessels.  The  circulation  lasts  during 
the  whole  of  intra-uterine  life,  but  gives  way  at  birth  to  the  adult  circula- 
tion, the  change  being  made  possible  by  the  development  of  the  circulatory 
apparatus. 

The  heart  appears  as  a  mass  of  cells  coming  off  from  the  anterior  por- 
tion of  the  intestine  ;  its  central  part  liquefies,  and  pulsations  soon  begin. 
The  heart  is  at  first  tubular,  receiving  posteriorly  the  venous  trunks  and 
giving  off  anteriorly  the  arterial  trunks.  It  soon  becomes  twisted  upon 
itself,  so  that  the  two  extremities  lie  upon  the  same  plane. 

The  heart  now  consists  of  a  single  auricle  and  a  single  ventricle.  A 
septum,  growing  from  the  apex  of  the  ventricle,  divides  into  two  cavities, 
a  right  and  a  left.  The  auricles  also  become  partly  separated  by  a  septum, 
which  is  perforated  by  the  foramen  ovale.  The  arterial  trunk  becomes 
separated,  by  a  partition,  into  two  canals,  which  become,  ultimately,  the 
aorta  and  the  pulmonary  artery.  The  auricles  are  separated  from  the  ven- 
tricles by  incomplete  septa,  through  which  the  blood  passes  into  the 
ventricles. 

Arteries. — The  aorta  arises  from  the  cephalic  extremity  of  the  heart  and 
divides  into  two  branches,  which  ascend,  one  on  each  side  of  the  intestine, 
and  unite  posteriorly  to  form  the  main  aorta  ;  posteriorly  to  these  first  aortic 
arches  four  others  are  developed,  so  that  there  are  five  altogether  running 
along  the  visceral  arches.  The  two  anterior  soon  disappear.  The  third 
arch  becomes  the  internal  carotid  and  the  external  carotid  ;  a  part  of  the 
fourth  arch,  on  the  right  side,  becomes  the  subclavian  artery,  and  the 
remainder  atrophies  and  disappears,  but  on  the  left  side  it  enlarges  and 
becomes  the  permanent  aorta  ;  theji/th  arch  becomes  the  pulmonary  artery 


262  HUMAN   PHYSIOLOGY. 

on  the  left  side.     The  communication  between  the  pulmonary  artery  and 
the  aorta,  the  ductus  arteriosus,  disappears  at  an  early  period. 

Veins. — The  venous  system  appears  first  as  two  short,  transverse  veins, 
the  canals  of  Cuvier,  formed  by  the  union  of  the  vertebral  veins  and  the 
cardinal  veins,  which  empty  into  the  auricle.  The  inferior  vena  cava  is 
formed,  as  the  kidneys  develop,  by  the  union  of  the  renal  veins,  which,  in 
a  short  time,  receive  branches  from  the  lower  extremities.  The  subclavian 
veins  join  the  jugular  as  the  upper  extremities  develop.  The  heart  descends 
in  the  thorax,  and  the  canals  of  Cuvier  become  oblique  ;  they  shortly  com- 
municate by  a  transverse  duct,  which  ultimately  becomes  the  left  innominate 
vein.  The  left  canal  of  Cuvier  atrophies  and  becomes  a  fibrous  cord.  A 
transverse  branch  now  appears,  which  carries  the  blood  from  the  left  cardiac 
vein  into  the  right,  and  becomes  the  vena  azygos  minor ;  the  right  cardiac 
vein  becomes  the  vena  azygos  major. 

Circulation  of  Blood  in  the  Fetus. — The  blood  returning  from  the 
placenta,  after  having  received  oxygen  and  being  freed  from  carbonic  acid, 
is  carried  by  the  umbilical  vein  to  the  under  surface  of  the  liver ;  here  a 
portion  of  it  passes  through  the  ductus  venosus  into  the  ascending  vena  cava, 
while  the  remainder  flows  through  the  liver  and  passes  into  the  vena  cava 
by  the  hepatic  veins.  When  the  blood  is  emptied  into  the  right  auricle,  it 
is  directed  by  the  Eustachian  valve  through  the  foramen  ovale,  into  the  left 
auricle,  thence  into  the  left  ventricle,  and  so  into  the  aorta  and  to  all  parts  of 
the  system.  The  venous  blood  returning  from  the  head  and  upper  extremities 
is  emptied,  by  the  superior  vena  cava,  into  the  right  auricle,  from  which  it 
passes  into  the  right  ventricle,  and  thence  into  the  pulmonary  artery.  Owing 
to  the  condition  of  the  lung  only  a  small  portion  flows  through  the  pulmo- 
nary capillaries,  the  greater  part  passing  through  the  ductus  arteriosus,  which 
opens  into  the  aorta  at  a  point  below  the  origin  of  the  carotid  and  subclavian 
arteries.  The  mixed  blood  now  passes  down  the  aorta  to  supply  the  lower 
extremities,  but  a  portion  of  it  is  directed,  by  the  hypogastric  arteries,  to 
the  placenta,  to  be  again  oxygenated. 

At  birth,  the  placental  circulation  gives  way  to  the  circulation  of  the 
adult.  As  soon  as  the  child  begins  to  breathe,  the  lungs  expand,  blood 
flows  freely  through  the  pulmonary  capillaries,  and  the  ductus  arteriosus 
begins  to  contract.  The  foramen  ovale  closes  about  the  tenth  day.  The 
umbilical  vein,  the  ductus  venosus,  and  the  hypogastric  arteries  become 
impervious  in  several  days,  and  ultimately  form  rounded  cords. 


TABLE  OF  PHYSIOLOGIC  CONSTANTS. 


Mean  height  of  male,  5  feet  d%  inches  ;  of  female,  5  feet  2  inches. 
Mean  weight  of  male,  145  pounds  ;  of  female,  121  pounds. 
Number  of  chemic  elements  in  the  human  body  :  from  16  to  18. 
Number  of  proximate  principles  in  the  human  body  :  about  100. 
Amount  of  water  in  the  body  weighing  145  pounds  :   109  pounds. 
Amount  of  solids  in  the  body  weighing  145  pounds  :  36  pounds. 
Amount  of  saliva  secreted  in  24  hours  :  about  3}^  pounds. 

Function  of  saliva  :  converts  starch  into  maltose. 

Active  principle  of  saliva  :  ptyalin. 
Amount  of  gastric  juice  secreted  in  24  hours  :  from  8  to  14  pounds. 

Function  of  gastric  juice  :  converts  albumin  into  peptone. 

Active  principles  of  gastric  juice  :  pepsin  and  hydrochloric  acid. 
Duration  of  digestion  :  from  3  to  5  hours. 
Amount  of  intestinal  juice  secreted  in  24  hours  :  about  I  pound. 

Function  of  intestinal  juice  :  converts  cane  sugar  into  dextrose  and 
levulose  ;  maltose  into  dextrose. 
Amount  of  pancreatic  juice  secreted  in  24  hours  :  about  1%  pounds. 

Active  principles  of  pancreatic  juice  :  trypsin,  amylopsin,  and 
steapsin. 

{I.   Splits  the  neutral  fats  into  fatty  acids  and  glycerin. 
2.   Converts  albumin  into  peptone. 
3.   Converts  starch  into  maltose. 
Amount  of  bile  poured  into  the  intestines  daily  :  about  2]A  pounds. 
I.  Assists  in  the  emulsification  of  fats. 

t-  2.   Stimulates  the  peristaltic  movements. 

r  unctions  :     \  r 

I    3.   Prevents  putrefactive  changes  in  the  food. 

I  4.   Promotes  the  absorption  of  fat. 
Amount  of  blood  in  the  body  :  from  16  to  18  pounds. 
Size  of  red  corpuscles  :  -^V 0  °f  an  inch. 
Size  of  white  corpuscles  :  ^jqtt  °f  an  inch. 
Shape  of  red  corpuscles  :  circular  biconcave  discs. 
Shape  of  white  corpuscles  :  globular. 

Number  of  red  corpuscles  in  a  cubic  millimeter  of  blood  (the  cubic  03  of 
an  inch)  :  5,000,000. 

263 


264  "human  physiology. 

Function  of  red  corpuscles  :  to  carry  oxygen  from  the  lungs  to  the  tissues. 
Frequency  of  the  heart's  pulsation  a  minute  :  72  on  the  average. 
Velocity  of  the  blood   movement   in  the  arteries  :    about    12  inches  a 

second. 
Length  of  time  required  for  the  blood  to  make  an  entire  circuit  of  the  vas- 
cular system  :  about  20  seconds. 
Amount  of  air  passing  in  and  out  of  the  lungs  at  each  respiratory  act : 

from  20  to  30  cubic  inches. 
Amount  of  air  that  can  be  taken  into  the  lungs  on  a  forced  inspiration  : 

no  cubic  inches. 
Amount  of  reserve  air  in  the  lungs  after  an  ordinary  expiration  :   100  cubic 

inches. 
Amount  of  residual  air  always  remaining  in  the  lungs  :  about  100  cubic 

inches. 
Vital  capacity  of  the  lungs  :  230  cubic  inches. 
Entire  volume  of  air  passing  in  and  out  of  the  lungs  in  24  hours  :  about 

400  cubic  feet. 
Composition  of  the  air:  nitrogen,  79.19  :  oxygen,  20.81,  in  100  parts. 
Amount  of  oxygen  absorbed  in  24  hours  :   18  cubic  feet. 
Amount  of  carbonic  acid  exhaled  in  24  hours  :   14  cubic  feet. 
Temperature  of  the  human  body  at  the  surface  :  98^°  F. 
Amount  of  urine  excreted  daily  :  from  40  to  50  ounces. 
Amount  of  urea  excreted  daily  :  512  grains. 
Specific  gravity  of  urine  :  from  1015  to  1025. 
Number  of  spinal  nerves  :  31  pairs. 
Number  of  roots   of  origin  :  two ;   1st,  anterior,  efferent ;  2d,  posterior, 

afferent. 
Rate  of  transmission  of  nerve  force  :  about  100  feet  a  second. 
Number  of  cranial  nerves  :   12  pairs. 

1.  Olfactory,  or  first  pair. 

2.  Optic,  or  second  pair. 

3.  Auditory,  or  eighth  pair. 

4.  Chorda  tympani  for  anterior  two  thirds 
of  tongue. 

5.  Branches  of  glasso-pharyngeal,  or  eighth 
pair,  for  posterior  one  third  of  tongue. 

Motor  nerves  to  eyeball  and  accessory  structures  :    motor  oculi,  or 

third  pair  ;  pathetic,  or  fourth  pair  ;  abducens,  or  sixth  pair. 
Motor  nerves  to  facial  muscles  :  portio  dura,  facial,  or  seventh  pair. 
Motor  nerve  to  tongue  :  hypoglossal,  or  twelfth  pair. 


Nerves  of  special  sense  : 


TABLE   OF    PHYSIOLOGIC   CONSTANTS.  265 

Motor  nerve  to  laryngeal  muscles  :  spinal  accessor)',  or  eleventh  pair. 
Sensory  nerve  of  the  face  :  trifacial,  or  fifth  pair. 
Sensor}'  nerve  of  the  pharynx  :  glossopharyngeal,  or  ninth  pair. 
Sensory  nerves  of  the  lungs,  stomach,  etc.:  pneumogastric,  or  tenth  pair. 
Length  of  spinal  cord  :   16  to  18  inches  ;  weight,  \yz  ounces. 
Point  of  decussation  of  motor  fibers  :  at  the  medulla  oblongata. 
Point  of  decussation  of  sensory  fibers  :  throughout  the  spinal  cord. 
Function  of  anterolateral  column  of  spinal  cord :  transmit  motor  im- 
pulses from' the  brain  to  the  muscles. 
Function  of  the  posterior  columns  :  assist  in  the  coordination  of  mus- 
cular movements. 
Function  of  the  medulla  oblongata  :  controls  the  functions  of  insaliva- 

tion,  mastication,  deglutition,  respiration,  circulation,  etc. 
Function  of  the  cerebellum  :    center  for  the  coordination  of  muscular 

movement. 
Function  of  the  cerebrum  :  center  for  intelligence,  reason,  and  will. 
Center  for  articulate  language  :  third  frontal  convolution  on  the  left  side 

of  cerebrum. 
Number  of  coats  to  the  eye  :  three  :  1st,  cornea  and  sclerotic  ;  2d,  choroid  ; 

3d,  retina. 
Function  of  iris  :  regulates  the  amount  of  light  entering  the  eye. 
Function  of  crystalline  lens  :  refracts  the  rays  of  light  so  as  to  form  an 

image  on  the  retina. 
Function  of  retina  :  receives  the  impressions  of  light. 
Function  of  membrana  tympani :  receives  and  transmits  waves  of  sound 

to  internal  ear. 
Function  of  Eustachian  tube  :  regulates  the  passage  of  air  into  and  from 

the  middle  ear. 
Function  of  semicircular  canals  :  assist  in  maintaining  the  equipoise  of 

the  body. 
Function  of  the  cochlea :    appreciates   the  shades  and  combinations  of 

musical  tones. 
Size  of  human  ovum  :  j^  of  an  inch  in  diameter. 
Size  of  spermatozoa  :  j-^jq  of  an  inch  in  length. 
Function  of  the  placenta  :  acts  as  a  respiratory  and  digestive  organ  for 

the  fetus. 
Duration  of  pregnancy  :  280  days. 

18 


TABLE  SHOWING  RELATION  OF  WEIGHTS  AND 
MEASURES  OF  THE  METRIC  SYSTEM  TO  APPROX- 
IMATE WEIGHTS    AND    MEASURES   OF   THE  U.   S. 


One  Myriameter 
One  Kilometer 
One  Hectometer 
One  Decameter 

One  Meter 

One  Decimeter 
One  Centimeter 


One  Millimeter         = 


One  Myriagram 
One  Kilogram 
One  Hectogram 
One  Decagram 

One  Gram 

One  Decigram 

One  Centigram 

One  Milligram 


One  Myrialiter 
One  Kiloliter 
One  Hectoliter 

One  Decaliter 

One  Liter 

One  Deciliter 

One  Centiliter 

One  Milliliter 


MEASURES  OF  LENGTH. 
=:     10,000  meters  = 

=       1,000      " 

=  IOO         ';  : 

=  IO        "  : 

{the  ten-millionth  part  of  a  \ 
quarter  of  the  Meridian  of  >  ■ 
the  Earth  J 

=     the  tenth  part  of  one  meter 
_  j  the  one-hundredth  part  oO 
_  \  one  meter  J  ' 

f  the    one- thousandth  part) 
\  of  one  meter  J 

WEIGHTS. 
=     10,000  grams 
=       1,000      ". 
=  100      " 

=  10 

_  (  the  weight  of  a  cubic  cen 
_  \  timeter  of  water  at  40  C 
==     the  tenth  part  of  a  gram 
_  f  the  hundredth  part  of  one 
~\gram 

_  f  the  thousandth  part  of  one  ") 
~  \  gram  j 

MEASURES  OF  CAPACITY 

{10  cubic    Meters  or  the^ 
measures  of  I  o  Milliers  of  j-  = 
water  J 


32,800       feet. 
:    3,280         " 
328         " 
32.80    " 

:  39-368  inches. 

:     3.936 

:    °-393  (I)  inch. 
:    0-039  (25)     " 

z  26^  pounds  Troy. 


(«  << 


2% 

2)%  ounces       " 

2X/Z  drams        " 

J5.434  grains. 

1-543  (iK)     "■ 
0.154(1^)  grain. 


j  I  cubic  Meter  or  the  meas- ") 
\  ure  of  I  Miller  of  water  j 

{100  cubic  Decimeters  or  \ 
the  measure  of  I  Quintal  >- 
of  water  J 

{io  cubic  Decimeters  or 
the  measure  of  1  Myria- 
gram of  water 
1  cubic  Decimeter  or  the  ^ 
measure  of  I  Kilogram  > 
of  water 

{100  cubic  Centimeters  or 
the  measure  of  I  Hecto- 
gram of  water 
!io  cubic  Centimeters  or 
the  measure  of  1  Deca- 
gram of  water 
{I  cubic  Centimeter  or  the 
measure  of  I  Gram  of 
water 


:     O.OI5    (^)        « 

2,600     gallons. 
260 
26  " 

2.6  " 
2.1  pints. 
3.3  ounces. 

2.7  drams. 
16.2  minims. 


INDEX. 


A BDUCENS  NERVE, 
•**■    Aberration,  chromatic, 


-,  spheric, 


Absorption, 

by  lacteals, 

by  blood-vessels 

of  oxygen  in  respiration,  .    .    . 

Accommodation  of  the  eye,  .    . 
Adipose  tissue,  uses  of,  in  the  body,  . 
Adrenal  bodies,         .    .  .... 

Adult  circulation,  establishment  of,  at 
birth,    ...  ...... 

Air,  atmospheric,  composition  of,  .    . 
,  amount  exchanged  in  respira- 


changes  in,  during  respiration, 

Albumin,  uses  of,  in  the  body,     .    . 

Albuminoid  substances, 

Alcohol,  action  of,   .    .  .... 

Alimentary  canal,  development  of,  . 

principles,  classification  of,  .    . 

,  albuminous  principles,     .    .    . 

,  saccharine  principles,   .... 

,  oleaginous  principles,  .    .    . 

,  inorganic  principles  .    .    . 

Allantois,   development  and  function 

of, 

Amnion,  formation  of, 

Animal  heat, 

Anterior  columns  of  spinal  cord,  .    .    . 

Area,  germinal, 

Areo'ar  tissue,  

Arteries,  properties  of, 

Articulations, 

-,  classification  of, 


>AGE 

187 
235 
235 
in 

115 
"5 
141 

233 

4i 

154 


262 
140 


Asphyxia, 
Astigmatism  .  .  . 
Axis,  cerebro-spinal,  .  . 
cylinder  of  nerves. 


139 
140 


90 
259 


254 
254 
143 
182 

253 

41 

131 

46 

47 
142 

234 
171 

73 


PAGE 

Blood  pressure, 132 

Bone,  structure  of,      44 

Burdach,  column  of, 174 


CANALS  OF  CUVIER,  .... 
Capillary  blood-vessels,,      .    .    . 

Capsule,  internal, 

,  external, 

Cardiac  cycle, 

Cartilage, 

Caudate  nucleus, 

Cells,  structure  of, 

,  manifestation  of  life  by,. 

of  anterior  horns  of  gray  matter, 

Center  for  articulate  language,  .... 

Cerebellum, 

-,  forced  movements  of, 


"DILE,         no 

■^     Bladder,  urinary-, 155 

Blastodermic  membranes, 253 

Blood, 119 

,  composition  of,  plasma,  .    .    .  120 

,  coagulation  of. 123 

,  coloring  matter  of,.           .        .  121 

,  changes  in,  during  respiration  142 

,  circulation  of, 125 

,  rapidity  of  flow  in  arteries,  .  .  133 

,  rapidity  of  flow  in  capillaries,  133 

,  corpuscles, 121 

,  origin  of, 122 


Cerebral  vesicles  of  embryo, 

Cerebrum, 

,  fissures  and  convolutions,  .    . 

,  functions  of, 

,  localization  of  functions,  .    .    . 

,  motor  area  of, 

,  special  centers  of,  .    . 

Chemic  composition  of  human  body,  . 

Chorda  dorsalis, ... 

tympani  nerve,  course  and  func- 
tion of,  

Chorion, 

Chyle,      .    . 

Ciliary  muscle, 

Circulation  of  blood, 

Claustrum, 

Cochlea, 

Columns  of  spinal  cord, .  .  .    . 

Connective  tissues,  physiologic  prop- 
erties of,  .   .  

Corium, 

Corpora  Wolffiana, 

quadrigemina,  .    .        

Corpus  luteum, 

striatum, . 

Corti,  organ  of, 

Cranial  nerves, 

Crura  cerebri,        

Crystalline  lens, 


262 

133 
204 
204 
128 
43 
204 

33 
35 
173 
216 
205 
206 

257 
207 
208 
213 
214 
214 
215 
15 
258 

191 

255 
117 

234 
125 
204 
243 

174 

45 
167 
260 
203 
250 
204 
244 
183 
202 
230 


T-\ECIDUAL  MEMBRANE,  . 


Decussation  of  motor  and   sen- 
sory fibers,  175 

Deglutition,    ...          _ 99 

,  nervous  circle  of, 199 


267 


268 


INDEX. 


PAGE 

Development  of  accessory  structures 

of  embryo 252 

Digestion, .  95 

Ductuslarteriosus, 262 

venosus,  .   .       262 

fTAR, 237 

■*-'     Electrotonus, 85 

Embryo,  development  of, 257 

Embryology, 248 

Endolymph, 244 

Epididymis, ,   .  251 

Eustachian  tube, 239 

Excretion, 155 

Eye, 225 

,  refracting  apparatus  of,       .  231 

,  blind  spot  of, 236 

"FACIAL  NERVE, 189 

■*■ paralysis,  symptoms  of,  .  190 

Fallopian  tubes,               24^ 

Fat,  uses  of,  in  the  body, 89 

Feces,' 111 

Female  organs  of  generation,    ....  247 

Fissures  and  convolutions  of  brain,   .  208 

Foods  and  dietetics,            86 

,  animal, 93 

,  vegetable, 94 

,  cereal,        94 

,  percentage,  composition  of,    .  94 

,  daily  amount  required,            .  91 

,  albuminous  principles  of,     .   .  88 

,  saccharine  principles  of,  ...  89 

,  oleaginous  principles  of,      .    .  89 

,  inorganic  principles  of,    .    .    .  89 

Fovea  centralis, 234 

f*ALVANIC      CURRENTS, 

^-*     effect  on  nerves, 85 

Ganglia, ....  219 

,  ophthalmic, 219 

,  Gasserian,                        ....  219 

,  spheno-palatine, 219 

.  otic, 219 

,  submaxillary, 219 

,  semilunar, ...                .  220 

Gases  of  the  intestine in 

Gastric  digestion, 101 

juice, 101 

,  action  of, .    .  105 

Generation,  male  organs  of, 251 

,  female  organs  of, 248 

Globules  of  the  blood, 121 

of  the  lymph 119 

Glomeruli  of  the  kidneys, 155 

Glosso-pharyngeal  nerve,              .    .    .  192 

Glottis,  respiratory  movements  of,  .    .  138 

Glycogen,    .        .                          ....  165 

Glycogenic  function  of  the  liver,  .  166 

Goll,  column  of,    .    .    .               ....  174 

Graafian  follicles, 247 

HAIR' l69 

■*■■*■     Hearing,  sense  of,       ....  237 

Heart, 125 


PAGE 

Heart,  valves  of, 128 

,  sounds  of, 129 

— — — ,    influence    of    pneumogastric 

nerve  upon, 131 

,  ganglia  of,   .    .    .           ....  130 

,  force  exerted  by  left  ventricle,  130 

,  work  done  by,       130 

,  course  of  blood  through,  .    .    .  126 

,  influence  of   nervous  system 

upon, 131 

Hemoglobin, 121 

Hyaloid  membrane, 230 

Hypermetropia, 235 

Hypoglossal  nerve, 196 

Hypophysis  cerebri, 153 

TNCUS  BONE, 238 

■*■     Insalivation,       .           96 

,  nervous  circle  of, 99 

Inspiration,  movements  of  thorax  in,  .  137 

Internal  capsule,  .    .           .    .           .    .  204 

,  results  of  injury  to,  .    .  204 

secretions, 150 

Intestinaljuice, 107 

Iris, .    .  227 

,  action  of, 235 


K 


IDNEYS, 

,  excretion  of  urine  by, 


155 
J59 


T    ABYRINTH  OF  INTERNAL 

"L/    ear, 243 

,  function  of  cochlea, 244 

,  function  of  semicircular  canals,  244 

Language,  articulate,  center  for,  .  .    .  216 

Larynx,               ...  245 

Lateral  columns  of  spinal  cord,    .    .    .  174 

Laws  of  muscular  contraction,     ...  85 

Lens,  crystalline,             230 

Lime  phosphate, 29 

Liver, 163 

,  secretion  of  bile  by, 165 

,  glycogenic  function  of,    ...  166 

,  elaboration  of  blood,     ....  165 

cells, 161 

Localization  of  functions  in  cerebrum,  214 

Lungs,         •  135 

,  changes  in  blood  while  passing 

through, 142 

Lymph, ....  117 

Lymphatic  glands, 113 

vessels,  origin  and  course  of,  .  113 

TWTALLEUS  BONE, 258 

■"•*■     Mammary  glands, 148 

Mastication,                      95 

,  nervous  circle  of,        96 

,  muscles  of, 95 

Medulla  oblongata,     .                       .    .  197 

,  properties  and  functions  of,  .  199 

Membrana  tympani,    ...               .    .  238 

Menstruation, 240 

Middle  ear, .  2^8 


INDEX. 


•269 


PAGE 

Milk, 149 

Motor  centers  of  cerebrum 214 

Muscles,  properties  of, 51 

,  changes  in,  during  contraction,  57 

,  special  physiology  of,  ...    .  63 

Muscle-fiber,  histology  of,     .    .       .    .  52 

Myopia, 235 

TSJERVE,  OLFACTORY,    .       .  183 

*  '     ,  optic, 184 

,  motor  oculi 185 

,  pathetic, 186 

,  trigeminal, 187 

,  abducens, 187 

,  facial, 189 

,  auditory, 191 

,  glosso-pharyngeal, 192 

,  pneumogastric,      192 

,  spinal  accessory, igo 

,  hypoglossal, 196 

cells,  structure  of,          ....  70 

fibers,  structure  of 72 

,  terminations  of,     ...  76 

force,  rate  of  transmission  of,  .  83 

roots,  function  of  anterior  and 

posterior,             77 

tissue,  histology  of, 69 

trunks,  structure  of,   .    .       .    .  73 

Nerves,  centrifugal  and  centripetal.  .  77 

,  classification  of,     .    .            .    .  75 

,  relation  of,  to  central  nervous 

system,        77 

,  development  and  nutrition  of,  78 

,  cranial,  .    .           183 

,  decussation  of  motor  and  sen- 
sory,       175 

,  vaso-motor,         .    .        ....  200 

,  properties  and  functions  of,    .  75 

,  spinal,           174 

Nervous  tissue,  physiology  of,     ...  69 

,  cerebrospinal 171 

,  sympathetic, 220 

Neurone, 70 

Nucleus  caudatus, 204 

,  lenticularis, 204 

QLFACTORY    NERVES,  ...  183 

^•^     Ophthalmic  ganglion, 181 

Optic  nerves, 184 

,  thalamus, 204 

,  functions  of,    .    .    .  ,    .        .    .  205 

Organs  of  Corti, 244 

Otic  ganglion,       219 

Ovaries, 248 

Ovum, 248 

,  discharge  of,  from  the  ovary,  •  248 

Oxygen,    absorption     of,    by    hemo- 
globin,       122 

OANCREATIC  JUICE 107 

■*■       Patheticus  nerve, 186 

Peptones, 105 

Perilymph, 243 

Perspiration, 170 


PAGE 

Petrosal  nerves,  large  and  small.     .   .  190 

Phonation,  .    .       247 

Physiology,  definition  of, 9 

Placenta,  formation  and  function  of,  .  256 

Pleura,     .    .               ...           ....  136 

Pneumogastric  nerve, 192 

Pons  Varolii, 201 

Portal  vein, .    .        .    .  161 

Posterior  columns  of  spinal  cord,  .    .  182 

,  functions  of, 182 

Prehension, 95 

Presbyopia,        .            235 

Pressure  of  blood  in  arteries,    ....  132 

Proximate  principles,     .    .        ....  16 

,  inorganic,     .            29 

,  organic,  non-nitrogenized,  .    .  16 

,  organic,  nitrogenized,   ....  23 

,  of  waste, 32 

,  quantity  of  chemic  elements  in 

body, 16 

Ptyalin, 98 

Pulse,                      132 

Pyramidal  tracts, 174 

DED         CORPUSCLES         OF 

■*^"     blood,  121 

Reflex  movements  of  spinal  cord,  .    .  188 

action,  laws  of, 177-181 

Reproduction, 248 

Respiration, 135 

,  movements  of, 137 

,  types  of, 139 

,  nervous  circle  of, 138 

Retina, 229 

Rigor  mortis,   ..'...      54 

OALIVA, .  98 

***     Sebaceous  glands,       169 

Secretion, .      .    .        155 

Semen,           252 

Semicircular  canals 243 

Sight,  sense  of, 226 

Skeleton,            46 

Skin 168 

Smell,  sense  of, 225 

Sounds  of  heart 129 

Spermatozoa, 252 

Spheno-palatine  ganglion, 2x9 

Spinal  accessory  nerve, 195 

cord            171 

cord,  membranes  of, 171 

,  structure  of  white  matter,  .    .  173 

,  structure  of  gray  matter,      .    .  173 

,  properties  of, 174 

,  function  of,  as  a  conductor,  .  .  181 

,  as  an  independent  center,    .    .  176 

,  decussation  of  motor  and  sen- 
sory fibers,                     175 

,  reflex  action  of,      178 

,  special  centers  of, 181 

,  paralysis  from  injuries  of,    .    .  182 

,  nerves,  origin  of 174 

,  course  of  anterior  and  posterior 

roots  of, 175 


270 


INDEX. 


PAGE 

Spleen, 151 

Starvation,  phenomena  of, 86 

Stomach,       .    .              100 

Submaxillary  ganglion 219 

Sudoriparous  glands, 170 

Sugar,  uses  of,  in  the  body, 89 

Supra-renal  capsules, 154 

Sympathetic  nervous  system,  ....  218 
,  properties  and  functions  of,    .  219 

npASTE,  SENSE  OF,   .....  223 

■*•      ,  nerve  of,     . 224 

Teeth, 95 

Tensor  tympani  muscle, 241 

Testicles,        .    .           251 

Thoracic  duct, 115 

Thorax,  enlargement  of,  in  inspiration,  137 

Thyroid  gland 151 

Tissues,  physiology  of, 39 

Tongue, 223 

,  motor  nerve  of, 224 

,  sensory  nerve  of, 224 

Touch,  sense  of, 292 

Tiirck,  column  of, 174 


PAGE 

TTMBILICAL  CORD 254 

*"*'      Urea,                .    .  167 

Uric  acid,           . .  161 

Urination,  nervous  mechanism  of,  .    .  159 

Urine,          159 

. ,  composition  of,  ......    .  160 

,  average  quantity  of  constitu- 
ents secreted  daily,      160 

Uterus, .  249 

TT-APOR,         WATERY,         OF 

"      breath, 150 

Vascular  glands, .  150 

system,  development  of,  260 

Vaso-motor  nerves,  origin  of,       ...  200 

Veins,  .    .        133 

Vertebral  column, 49 

Vesiculse  seminalesj 251 

Vision,  psychic  center  for, 21S 

Vital  capacity  of  lungs, 140 

Vocal  cords, 246 

Voice, 245 

TX7ATER,   AMOUNT    OF,    IN 

vv      body, 29 

I  Wolffian  bodies, 260 


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2 


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3 


Morris'  Anatomy 

Rewritten — Revised — Improved 
WITH  MANY  NEW  ILLUSTRATIONS 


Out  of  102  of  the  leading  medical  schools  60  recommend 
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McMurrich — Embryology 

Nearly  Ready.    276  Illustrations 


A  Text-Book  for  Medical  Students.  By  J.  PlAYFAIR 
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5 


SUBJECT  [INDEX. 


Gould's  Medical  Dictionaries, 
Morris'  Anatomy,  New  Edition, 
Compends  for  Students, 


Page  12 
Page  4 
Page  26 


SUBJECT  PAGE 

Alimentary  Canal  (see  Surgeiy)  23 

Anatomy 7 

Anesthetics 18 

Autopsies  (see  Pathology) 20 

Bacteriology  (see  Pathology)..  20 

Bandaging  (see  Surgery) 23 

Blood,  Examination  of 20 

Brain  8 

Chemistry.     Physics 8 

Children,  Diseases  of 10 

Climatology 18 

Clinical  Charts 24 

Compends  26 

Consumption  (see  Lungs) 15 

Cyclopedia  of  Medicine 12 

Dentistry 11 

Diabetes  (see  Urin.  Organs)..  24 

Diagnosis 10 

Diagrams  (see  Anatomy) 7 

Dictionaries,  Cyclopedias 12 

Diet  and  Food 18 

Disinfection  • 15 

Dissectors 7 

Ear 13 

Electricity 13 

Embryology 7 

Emergencies 23 

Eye 13 

Fevers 14 

Food 18 

Formularies 21 

Gynecology 25 

Hay  Fever 24 

Heart 14 

Histology 14 

Hydrotherapy 18 

Hygiene 15 

Hypnotism 8 

Insanity  8 

Intestines 22 

Latin,  Medical  (see  Miscella- 
neous and  Pharmacy) 18,20 

Life  Insurance 18 

Lungs 75 

Massage 16 

Materia  Medica 16 


SUBJECT.  PAGE 

Mechanotherapy 16 

Medical  Jurisprudence 17 

Mental  Therapeutics 8 

Microscopy  17 

M  ilk  Analysis  (see  Chemistry)      8 

Miscellaneous  18 

Nervous  Diseases  18 

Nose 24 

Nursing 19 

Obstetrics 20 

Ophthalmology *3 

Organotherapy 18 

Osteology  (see  Anatomy) 7 

Pathology 20 

Pharmacy 20 

Physical  Diagnosis n 

Physical  Training 16 

Physiology  21 

Pneumotherapy 18 

Poisons  (see  Toxicology) 17 

Practice  of  Medicine 22 

Prescription  Books  (Pharm'y),  21 

Refraction  (see  Eye) 13 

Rest 18 

Sanitary  Science 15 

Skin 23 

Spectacles  (see  Eye) 13 

Spine  (see  Nervous  Diseases)  18 

Stomach 22 

Students'  Compends 26 

Surgery  and  Surg'l  Diseases,  23 

Technological  Books 8 

Temperature  Charts 24 

Therapeutics 16 

Throat  24 

Toxicology 17 

Tumors  (see  Surgery) 23 

U.  S.  Pharmacopoeia 21 

Urinary  Organs 24 

Urine 24 

Venereal  Diseases 25 

Veterinary  Medicine 25 

Visiting  Lists,  Physicians'. 
(Send for  Special  Circular.) 

Water  Analysis.. 15 

Women,  Diseases  of. 25 


Self-Examination  for  Medical  Students.  3500  Questions  on 
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correct  replies  will  be  found.  Together  with  Questions  from  State 
Examining  Boards.    3d  Edition.     Paper  Cover,  10  cts. 


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ANATOMY.     EMBRYOLOGY. 

MORRIS.  Text-Book  of  Anatomy.  Revised  and  Enlarged  Edi- 
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CAMPBELL.  Dissection  Outlines.  Based  on  Morris' Anatomy. 
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HOLDEN.     Landmarks.    Medical  and  Surgical.    4th  Ed.  .75 

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I,  Upper  and  Lower  Extremity.  $3 .00 

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MACALISTER.  Human  Anatomy.  Systematic  and  Topograph- 
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McMURRICH.     Embryology.    270  Illustrations.     Nearly  Ready. 

MARSHALL.  Physiological  Diagrams.  Eleven  Life-Size 
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WILSON.    Anatomy,    nth  Edition.    429  Illus.,  26  Plates.      $5.00 

8-1-02. 


SUBJECT  CATALOGUE. 


BRAIN  AND  INSANITY  (see  also 
Nervous  Diseases). 

BLACKBURN.  A  Manual  of  Autopsies.  Designed  for  the  Use 
of  Hospitals  for  the  Insane  and  other  Public  Institutions.  Ten  full- 
page  Plates  and  other  Illustrations.  $i-*5 

CHASE.     General  Paresis.     Illustrated.    Just  Ready.  $i  75 

DERCUM.      Mental    Therapeutics,    Rest,   Suggestion.      See 

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HORSLEY.  The  Brain  and  Spinal  Cord.  The  Structure  and 
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IRELAND.    The  Mental  Affections  of  Children.    2d  Ed.    $4.00 

LEWIS  (BEVAN).  Mental  Diseases.  A  Text-Book  Having 
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MANN.     Manual  of  Psychological  Medicine.  $3.00 

PERSHING.  Diagnosis  of  Nervous  and  Mental  Disease. 
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REGIS.  Mental  Medicine.  Authorized  Translation  by  H.  M. 
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TUKE.  Dictionary  of  Psychological  Medicine.  Giving  the 
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methods  for  the  Detection  of  Impurities,  Adulterations,  etc.   .8vo. 

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Vol.  II,  Part  III.  Terpenes,  Essential  Oils,  Resins,  Camphors,  etc. 
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Coffee,  Cocoa,  etc.    8vo.    2d  Edition.  ^4-5° 

Vol.  Ill,  Part  III.  Vegetable  Alkaloids,  Non-Basic  Vegetable  Bitter 
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BAILEY  AND  CADY.     Qualitative  Chemical  Analysis.    $1.25 


MEDICAL  BOOKS.  9 


BARTLEY.  Medical  and  Pharmaceutical  Chemistry.  A 
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Illustrations,  Glossary,  and  Complete  Index.     5th  Edition.         $3-oo 

BARTLEY.  Clinical  Chemistry.  The  Examination  of  Feces, 
Saliva,  Gastric  Juice,  Milk,  and  Urine.  $1.00 

BLOXAM.  Chemistry,  Inorganic  and  Organic.  With  Experi- 
ments.   9th  Ed..  Revised.     381  Engravings.  Preparing. 

BUNGE.  Physiologic  and  Pathologic  Chemistry.  From  the 
Fourth  German  Enlarged  Edition.    Just  Ready.  J3.C0 

CALDWELL.  Elements  of  Qualitative  and  Quantitative 
Chemical  Analysis.    3d  Edition,  Revised.  $1.00 

CAMERON.     Oils  and  Varnishes.    With  Illustrations.  $2.25 

CAMERON.     Soap  and  Candles.    54  Illustrations.  $2.00 

CLOWES  AND   COLEMAN.      Quantitative  Analysis.      5th 

Edition.     122  Illustrations.  $3-5o 

COBLENTZ.     Volumetric  Analysis.    Illustrated.  $r.a5 

CONGDON.     Laboratory  Instructions  in  Chemistry.     With 

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GARDNER.  The  Brewer,  Distiller,  and  Wine  Manufac- 
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GRAY.  Physics.  Volume  I.  Dynamics  and  Properties  of  Matter. 
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OETTEL.    Exercises  in  Electro-Chemistry.    Illustrated.       .75 

OETTEL.    Electro-Chemical  Experiments.    Illustrated.         .75 

RICHTER.  Inorganic  Chemistry.  5th  American  from  10th  Ger- 
man Edition.  Authorized  translation  by  Edgar  F.  Smith,  m.a., 
ph.d.     89  Illustrations  and  a  Colored  Plate.  ^I-75 

RICHTER.  Organic  Chemistry.  3d  American  Edition.  Trans, 
from  the  8th  German  by  Edgar  F.  Smith.  Illustrated.  2  Volumes. 
Vol.    I.    Aliphatic  Series.     625  Pages.  $3-°o 

Vol.  II.    Carbocyclic  Series.    671  Pages.  $3-°° 


10  SUBJECT  CATALOGUE. 

ROCKWOOD.  Chemical  Analysis  for  Students  of  Medicine, 
Dentistry,  and  Pharmacy.     Illustrated.  $1-50 

SMITH.    Electro-Chemical  Analysis.    2d  Ed.    28  Illus.       $1.25 

SMITH  AND  KELLER.  Experiments.  Arranged  for  Students 
in  General  Chemistry.     4th  Edition.     Illustrated  .60 

SUTTON.  Volumetric  Analysis.  A  Systematic  Handbook  for 
the  Quantitative  Estimation  of  Chemical  Substances  by  Measure, 
Applied  to  Liquids,  Solids,  and  Gases.  8th  Edition,  Revised.  112 
Illustrations.  #5.00 

SYMONDS.    Manual  of  Chemistry.    2d  Edition.  #2.00 

TRAUBE.    Physico-Chemical  Methods.    Translated  by  Hardin. 

97  Illustrations.  $1.50 

THRESH.    "Water  and  Water  Supplies.    3d  Edition.  $2.00 

ULZER  AND  FRAENKEL.    Chemical  Technical  Analysis. 

Translated  by  Fleck.     Illustrated.  $1-25 

WOODY.    Essentials    of    Chemistry    and    Urinalysis.      4th 

Edition.     Illustrated.  $1-50 

***  Special  Catalogue  of  Books  on  Chemistry  free  upon  application. 

CHILDREN. 

HATFIELD.  Compend  of  Diseases  of  Children.  With  a 
Colored  Plate.     3d  Edition.    In  Press.  .80;   Interleaved.  $1.00 

IRELAND.  The  Mental  Affections  of  Children.  Idiocy, 
Imbecility,  Insanity,  etc.     2d  Edition.  #4.00 

POWER.  Surgical  Diseases  of  Children  and  their  Treat- 
ment by  Modern  Methods.    Illustrated.  $2.50 

STARR.  The  Digestive  Organs  in  Childhood.  The  Diseases  of 
the  Digestive  Organs  in  Infancy  and  Childhood.  3d  Edition,  Rewrit- 
ten and  Enlarged.     Illustrated.  ftj.oo 

STARR.  Hygiene  of  the  Nursery.  Including  the  General  Regi- 
men and  Feeding  of  Infants  and  Children,  and  the  Domestic  Manage- 
ment of  the  Ordinary  Emergencies  of  Early  Life,  Massage,  etc.  6th 
Edition.     25  Illustrations.  $1.00 

SMITH.    Wasting  Diseases  of  Children.    6th  Edition.        $2.00 

TAYLOR  AND  WELLS.  The  Diseases  of  Children.  2d  Edi- 
tion, Revised  and  Enlarged.     Illustrated.     8vo.  #4.5° 

"  It  is  well  worthy  the  careful  study  of  both  student  and  practitioner, 
and  can  not  fail  to  prove  of  great  value  to  both.  We  do  not  hesitate 
to  recommend  it." — Boston  Medical  and  Surgical  Journal. 

DIAGNOSIS. 

BROWN.  Medical  Diagnosis.  A  Manual  of  Clinical  Methods. 
4th  Edition.     112  Illustrations.  Cloth,  #2.25 

DA  COSTA.  Clinical  Hematology.  A  Practical  Guide  to  Exam- 
ination of  Blood.  6  Colored  Plates.  48  other  Illustrations.  Just 
Ready.  Cloth,  $5.00;  Sheep,  $6.00 

EMERY.  Bacteriological  Diagnosis.  2  Colored  Plates  and  32 
other  Illustrations.    Just  Ready.  $1.50 

MEMMINGER.   Diagnosis  by  the  Urine.  2d  Ed.  24  Illus.  $1.00 


MEDICAL  BOOKS.  11 


PERSHING.  Diagnosis  of  Nervous  and  Mental  Diseases. 
Illustrated.  5I25 

STEELL.     Physical  Signs  of  Pulmonary  Disease.  $1-25 

TYSON.  Hand-Book  of  Physical  Diagnosis.  For  Students  and 
Physicians.  By  the  Professor  of  Clinical  Medicine  in  the  University 
of  Pennsylvania.  Illus.  4th  Ed.,  Improved  and  Enlarged.  With 
Two  Colored  and  55  other  illustrations.  $1.50 


DENTISTRY. 

Special  Catalogue  of  Dental  Books  sent  free  upon  application. 

BARRETT.  Dental  Surgery  for  General  Practitioners  and 
Students  of  Medicine  and  Dentistry.  Extraction  of  Teeth, 
etc.     3d  Edition.     Illustrated.  #1.00 

BROOMELL.  Anatomy  and  Histology  of  the  Human  Mouth 
and  Teeth.  Second  Edition,  Revised  and  Enlarged.  337  Hand- 
some Illustrations.  $4-5° 

FILLEBROWN.      A    Text-Book    of    Operative     Dentistry. 

Written  by  invitation  of  the  National  Association  of  Dental  Facul- 
ties.    Illustrated.  #2.35 

GORGAS.  Dental  Medicine.  A  Manual  of  Materia  Medica  and 
Therapeutics.    7th  Edition.  Cloth,  $4.00;  Sheep,  #5.00 

GORGAS.  Questions  and  Answers  for  the  Dental  Student. 
Embracing  all  the  subjects  in  the  Curriculum  of  the  Dental  Student. 
Octavo.  #6.00 

HARRIS.  Principles  and  Practice  of  Dentistry.  Including 
Anatomy,  Physiology,  Pathology,  Therapeutics,  Dental  Surgery, 
and  Mechanism.  13th  Edition.  Revised  by  F.  J.  S.  Gorgas,  m.d., 
d.d.s.     1250  Illustrations.  Cloth,  $6.00;  Leather,  $7.00 

HARRIS.  Dictionary  of  Dentistry.  Including  Definitions  of  Such 
Words  and  Phrases  of  the  Collateral  Sciences  as  Pertain  to  the  Art  and 
Practice  of  Dentistry.  6th  Edition.  Revised  and  Enlarged  by  Fer- 
dinand F.  S.  Gorgas,  m.d.,  d.d.s.         Cloth,  #5.00;  Leather,  $6.00 

RICHARDSON.  Mechanical  Dentistry.  7th  Edition.  Thor- 
oughly Revised  and  Enlarged  by  Dr.  Geo.  W.  Warren.  691  Illus- 
trations. Cloth,  $5. 00;  Leather,  #6.00 

SMITH.    Dental  Metallurgy,    ad  Edition.    Illustrated.    In  Press. 

TAFT.    Index  of  Dental  Periodical  Literature.  #2.00 

TOMES.    Dental  Anatomy.    Human  and  Comparative.    263  Illus- 
trations.    5th  Edition.  #4.00 
TOMES.    Dental  Surgery.    4th  Edition.    289  Illustrations.     $4.00 

WARREN.  Compend  of  Dental  Pathology  and  Dental  Medi- 
cine.    With  a  Chapter  on  Emergencies.    3d  Edition.    Illustrated. 

.80;  Interleaved,  $1.25 

WARREN.  Dental  Prosthesis  and  Metallurgy.  129  Ills.  £1.25 
WHITE.    The  Mouth  and  Teeth.    Illustrated.  .40 


12  SUBJECT  CATALOGUE. 

DICTIONARIES  AND  CYCLOPEDIAS 

GOULD.  The  Illustrated  Dictionary  ot  Medicine,  Biology 
and  Allied  Sciences.  Being  an  Exhaustive  Lexicon  of  Medicine 
and  those  Sciences  Collateral  to  it:  Biology  (Zoology  and  Botany), 
Chemistry,  Dentistry,  Parmacology,  Microscopy,  etc.,  with  many 
useful  Tables  and  numerous  fine  Illustrations.  1633  pages.  5th  Ed. 
Sheep  or  Half  Morocco,  $10.00  ;  with  Thumb  Index,  $11.00 
Half  Russia,  Thumb  Index,  $12. co 

GOULD.  The  Medical  Student's  Dictionary,  nth  Edition. 
Illustrated.  Including  all  the  Words  and  Phrases  Generally  Used 
inMedicine,  with  their  Proper  Pronunciation  and  Definition,  Based 
on  Recent  Medical  Literature.  With  Table  of  Eponymic  Terms  and 
Tests  and  Tables  of  the  Bacilli,  Micrococci,  Mineral  Springs,  etc., 
of  the  Arteries,  Muscles,  Nerves,  Ganglia,  Plexuses,  etc.  nth  Edi- 
tion. Enlarged  and  illustrated  with  a  large  number  of  Engravings. 
840  pages.  Half  Morocco,  $2.30;  with  Thumb  Index,  $3  00 

GOULD.  The  Pocket  Pronouncing  Medical  Lexicon.  4th  Edi- 
tion. (30,000  Medical  Words  Pronounced  and  Defined.)  Containing 
all  the  Words,  their  Definition  and  Pronunciation,  that  the  Medical, 
Dental,  or  Pharmaceutical  Student  Generally  Comes  in  Contact 
With;  also  Elaborate  Tables  of  Eponymic  Terms.  Arteries,  Muscles, 
Nerves,  Bacilli,  etc.,  etc.,  a  Dose  List  in  both  English  and  Metric 
Systems,  etc.,  Arranged  in  a  Most  Convenient  Form  for  Reference  and 
Memorizing.  Fourth  Edition,  Revised  and  Enlarged.  838 
pages.  Full  Limp  Leather,  Gilt  Edges,  $1.00  ;  Thumb  Index,  $1.25 
140,000  Copies  of  Gould's  Dictionaries  Have  Been  Sold. 

GOULD  AND  PYLE.  Cyclopedia  of  Practical  Medicine  and 
Surgery.  Seventy-two  Special  Contributors.  Illustrated. 
One  Volume.  A  Concise  Reference  Handbook  of  Medicine, 
Surgery,  Obstetrics,  Materia  Medica,  Therapeutics,  and  the  Various 
Specialties,  with  Particular  Reference  to  Diagnosis  and  Treatment. 
Compiled  under  the  Editorial  Supervision  of  George  M.  Gould, 
m.d.,  Author  of  "  An  Illustrated  Dictionary  of  Medicine,"  etc.; 
and  Walter  L.  Pyle,  m.d.,  Assistant  Surgeon  Wills  Eye 
Hospital  ;  formerly  Editor  "International  Medical  Magazine,"  etc., 
and  Seventy-two  Special  Contributors.  With  many  Illustrations. 
Large  Square  8vo,  to  correspond  with  Gould's  "  Illustrated  Dic- 
tionary." Full  Sheep  or  Half  Mor  ,$10.00;  with  Thumb  Index,  $11.00 
Half  Russia,  Thumb  Index,  $12.00  net. 

GOULD  AND  PYLE.  Pocket  Cyclopedia  of  Medicine  and 
Surgery.  Based  upon  above  book  and  uniform  in  size  with  "  Gould's 
Pocket  Dictionary." 

Full  Limp  Leather,  Gilt  Edges,  $1.00,  with  Thumb  Index,  $1.25 

HARRIS.  Dictionary  of  Dentistry.  Including  Definitions  of  Such 
Words  and  Phrases  of  the  Collateral  Sciences  as  Pertain  to  the  Art 
and  Practice  of  Dentistry.  6th  Edition.  Revised  and  Enlarged  by 
Ferdinand  J.  S.  Gorgas,  m.d.,  d.d.s.   Cloth,  $5.00;  Leather,  $6.00 

LONGLEY.     Pocket  Medical  Dictionary.  Cloth,  .75 

MAXWELL.  Terminologia  Medica  Polyglotta.  By  Dr. 
Theodore  Maxwell,  Assisted  by  Others.  $3.00 

The  object  of  this  work  is  to  assist  the  medical  men  ot  any  nationality 

In  reading  medical  literature  written  in  a  language  not  their  own. 

Each  term  is  usually  given  in  seven  languages,  viz. :  English,  French, 

German,  Italian,  Spanish,  Russian,  and  Latin. 

TREVES  AND  LANG.    German-English  Medical  Dictionary. 

Half  Calf,  $3.25 


MEDICAL  BOOKS.  13 


EAR  (see  also  Throat  and  Nose). 

BURNETT.     Hearing  and  How  to  Keep  It.    Illustrated.         .46 

DALBY.      Diseases  and  Injuries  of  the  Ear.    4th  Edition.     38 

Wood  Engravings  and  8  Colored  Plates.  $2.50 

HOVELL.  Diseases  ot  the  Ear  and  Naso-Pharynx.  Includ- 
ing Anatomy  and  Physiology  of  the  Organ,  together  with  the  Treat- 
ment of  the  Affections  of  the  Nose  and  Pharynx  which  Conduce  to 
Aural  Disease.     128  Illustrations.     2d  Edition.  f, 5.50 

PRITCHARD.  Diseases  of  the  Ear.  3d  Edition,  Enlarged. 
Many  Illustrations  and  Formulae.  $1.50 

ELECTRICITY. 

BIGELOW.  Plain  Talks  on  Medical  Electricity  and  Bat- 
teries. With  a  Therapeutic  Index  and  a  Glossary.  43  Illustra- 
tions.    2d  Edition.  $1.00 

HEDLEY.  Therapeutic  Electricity  and  Practical  Muscle 
Testing,     qq  Illustrations.  $2.50 

JACOBY.  Electrotherapy.  2  Vols.  Illustrated.  See  Cohen, 
Physiologic  Therapeutics ,  page  lb. 

JONES.   Medical  Electricity.  3d  Edition.  117  Illus.  I3.00 

EYE. 

A  Special  Circular  0/  Books  on  the  Eye  sent  free  upon  application. 

DONDERS.  The  Nature  and  Consequences  of  Anomalies  of 
Refraction.     With  Portrait  and  Illustrations.     Half  Morocco,  $1. 25 

FICK.  Diseases  of  the  Eye  and  Ophthalmoscopy.  Trans- 
lated by  A.  B.  Hale,  m.  d.  157  Illustrations,  many  of  which  are  in 
colors,  and  a  glossary.  Cloth,  $4.50 ;  Sheep,  $5.50 

GOULD  AND  PYLE.  Compend  of  Diseases  of  the  Eye  and 
Refraction.  Including  Treatment  and  Operations,  and  a  Section 
on  Local  Therapeutics.  With  Formulae,  Useful  Tables,  a  Glossary, 
and  m  Illus.,  several  of  which  are  in  colors.     2d  Edition,  Revised. 

Cloth,  .80;  Interleaved,  $1. 00 

GREEFF.  The  Microscopic  Examination  of  the  Eye.  Illus- 
trated. |I<25 

HARLAN.    Eyesight,  and  How  to  Care  for  It.     Illus.  .40 

HARTRIDGE.  Refraction.  104  Illustrations  and  Test  Types, 
nth  Edition,  Enlarged.  t1-5° 

HARTRIDGE.  On  the  Ophthalmoscope.  4th  Edition.  With 
4  Colored  Plates  and  68  Wood-cuts.  £1.50 

HANSELL  AND  REBER.  Muscular  Anomalies  ot  the  Eye. 
Illustrated.  $1.50 

HANSELL  AND  BELL.  Clinical  Ophthalmology.  Colored 
Plate  of  Normal  Fundus  and  120  Illustrations.  #1.50 

JENNINGS.  Manual  of  Ophthalmoscopy.  95  Illustrations  and 
1  Colored  Plate.  #1.50 


14  SUBJECT  CATALOGUE. 

MORTON.  Refraction  of  the  Eye.  Its  Diagnosis  and  the  Cor- 
rection of  its  Errors.     6th  Edition.  $1.00 

OH LE MANN.  Ocular  Therapeutics.  Authorized  Translation, 
and  Edited  by  Dr.  Charles  A.  Oliver.  $r-75 

PARSONS.  Elementary  Ophthalmic  Optics.  With  Diagram- 
matic Illustrations.  $2.00 

PHILLIPS.  Spectacles  and  Eyeglasses.  Their  Prescription 
and  Adjustment,    ad  Edition.     49  Illustrations.  $1.00 

SWANZY.  Diseases  of  the  Eye  and  Their  Treatment.  7th 
Edition,  Revised  and  Enlarged.  164  Illustrations,  1  Plain  Plate, 
and  a  Zephyr  Test  Card.  $2.50 

From  The  Medical  News. 

"  Swanzy  has  succeeded  in  producing  the  most  intellectually  con- 
ceived and  thoroughly  executed  resume  of  the  science  within  the 
limits  he  has  assigned  himself.  As  a  '  students'  handbook,'  small 
in  size  and  of  moderate  price,  it  can  hardly  be  equaled." 

THORINGTON.  Retinoscopy.  4th  Edition.  Carefully  Revised. 
Illustrated.  $1.00 

THORINGTON.  Refraction  and  How  to  Refract.  200  Illustra- 
tions, 13  of  which  are  Colored.     2d  Edition.  $1.50 

WALKER.  Students'  Aid  in  Ophthalmology.  Colored  Plate 
and  40  other  Illustrations  and  Glossary.  $i-5° 

WRIGHT.  Ophthalmology.  2d  Edition,  Revised  and  Enlarged. 
117  Illustrations  and  a  Glossary.  $3.00 


FEVERS. 

GOODALL  AND  WASHBOURN.    Fevers  and  Their  Treat- 
ment.    Illustrated.  $3-°° 

HEART. 

THORNE.    The  Schott  Methods  of  the  Treatment  of  Chronic 
Heart  Disease.    Fourth  Edition.    Illustrated.    Just  Ready.    $2.00 


HISTOLOGY. 

CUSHING.  Compend  of  Histology.  By  H.  H.  Cushing,  m.d., 
Demonstrator  of  Histology,  Jefferson  Medical  College,  Philadelphia. 
Illustrated.    Nearly  Ready.  .80;  Interleaved,  $1. 00 

STIRLING.  Outlines  of  Practical  Histology.  368  Illustrations. 
2d  Edition,  Revised  and  Enlarged.    With  new  illustrations.       $2.00 

STOHR.  Histology  and  Microscopical  Anatomy.  Edited  by 
A.  Schaper,  m.d.,  University  of  Breslau,  formerly  Demonstrator  of 
Histology,  Harvard  Medical  School.  Fourth  American  from  9th  Ger- 
man Edition,  Revised  and  Enlarged.     379  Illustrations.  #3  00 


MEDICAL  BOOKS.  15 


HYGIENE  AND  WATER  ANALYSIS. 

Special  Catalogue  of  Books  on  Hygiene  sent  free  upon  application. 

CANFIELD.     Hygiene  of  the  Sick-Room.    A  Book  for  Nurses 
and  Others.    Being  a  Brief  Consideration  of  Asepsis,  Antisepsis,  Dis- 
infection, Bacteriology,  Immunity,  Heating,  Ventilation,  etc.       $1.25 
CONN.     Agricultural  Bacteriology.     Illustrated.  £2.50 

COPLIN.  Practical  Hygiene.  A  Complete  American  Text-Book. 
138  Illustrations.     New  Edition.  Preparing. 

HARTSHORNE.     Our  Homes.     Illustrated.  .40 

KENWOOD.  Public  Health  Laboratory  Work.  116  Illustra- 
tions and  3  Plates.  $2.00 

LEFFMANN.  Select  Methods  in  Food  Analysis.  53  Illustra- 
tions and  4  Plates.  #2.50 

LEFFMANN.  Examination  ot  Water  for  Sanitary  and 
Technical  Purposes.     4th  Edition.    Illustrated.  $1.25 

LEFFMANN.  Analysis  of  Milk  and  Milk  Products.  Illus- 
trated. Second  Edition.  .  $1.25 
'LINCOLN.    School  and  Industrial  Hygiene.  .40 

McFARLAND.  Prophylaxis  and  Personal  Hygiene.  Care  of 
the  Sick.     See  Cohen.  Physiologic  Therapeutics, page  lb. 

OTTER.    The  Theory  and  Practice  of  Hygiene.    15  Plates 
nd  138  other  Illustrations.     8vo.     2d  Edition.  $7.00 

PA^RKES.  Hygiene  and  Public  Health.  By  Louis  C.  Parkes, 
M.p.     6th  Edition.     Enlarged.    Illustrated.  $3.00 

PARKES.  Popular  Hygiene.  The  Elements  of  Health.  A  Book 
for  Lay  Readers.     Illustrated.  $*-25 

ROSENAU.    Disinfection  and  Disinfectants.    Illustrated.  $2.00 
STARR.  The  Hygiene  of  the  Nursery.    Including  the  General 
Regimen  and  Feeding  of  Infants  and  Children,  and  the  Domestic 
Management  of  the  Ordinary  Emergencies  of  Early  Life,  Massage, 
etc.     6th  Edition.     25  Illustrations.  $1.00 

STEVENSON  AND  MURPHY.    A  Treatise  on  Hygiene.    By 

Various  Authors.     In    Three    Octave  Volumes.    Illustrated. 

Vol.  I,  $6.00;  Vol.  II,  J6.00;  Vol.  Ill,  $5.00 
%*  Each  Volume  sold  separately.   Special  Circular  upon  application. 

THRESH.     Water  and  Water  Supplies.    3d  Edition.  $2.00 

WILSON.    Hand-Book    of  Hygiene  and  Sanitary    Science. 

With  Illustrations.     8th  Edition.  $3°o 

WEYL.  Sanitary  Relations  of  the  Coal-Tar  Colors.  Author- 
ized Translation  by  Henry  Leffmann,  m.d.,  ph.d.  #1-25 


LUNGS  AND  PLEURAE. 

KNOPF.      Pulmonary  Tuberculosis.     Its   Modern  Prophylaxis 
and  Treatment  in  Special  Institutions  and  at  Home.     Illus.         $3.00 

STEELL.     Physical  Signs  of  Pulmonary  Disease.   Illus.  $1.25 


16  SUBJECT  CATALOGUE. 

MASSAGE— PHYSICAL  EXERCISE. 

OSTROM.  Massage  and  the  Original  Swedish  Move- 
ments. Their  Application  to  Various  Diseases  of  the  Body.  A 
Manual  for  Students,  Nurses,  and  Physicians.  Fifth  Edition,  En- 
larged.    115  Illustrations,  many  of  which  are  original.  #1.00 

MITCHELL  AND  GULICK.  Mechanotherapy,  Physical 
Education,  etc.  Illustrated.  See  Cohen,  Physiologic  Therapeu- 
tics, below. 

TREVES.     Physical  Education.    Its  Value,  Methods,  etc.         .75 


MATERIA    MEDICA    AND    THERA- 
PEUTICS. 

BIDDLE.  Materia  Medica  and  Therapeutics.  Including  Dose 
List,  Dietary  for  the  Sick,  Table  of  Parasites,  and  Memoranda  of 
New  Remedies.  13th  Edition,  Revised.  64  Illustrations  and  a 
Clinical  Index.  Cloth,  $4.00 ;  Sheep,  $5.00 

BRACKEN.     Outlines  of  Materia  Medica  and  Pharmacology.    #2.75 

COBLENTZ.  The  Newer  Remedies.  Including  their  Synonyms, 
Sources,  Methods  of  Preparation,  Tests,  Solubilities,  Doses,  etc. 
3d  Edition,  Enlarged  and  Revised.  #1.00 

COHEN.  Physiologic  Therapeutics.  Methods  other  than  Drug- 
Giving  useful  in  the  Prevention  of  Disease  a/nd  in  the  Treatment  of 
the  Sick.  Mechanotherapy,  Mental  Therapeutics,  Suggestion, 
Electrotherapy.  Climatology,  Hydrotherapy,  Pneumatotherapy, 
Prophylaxis,  Dietetics,  Organotherapy,  Phototherapy,  Mineral 
Waters,  Baths,  etc.  11  Volumes,  Octavo.  Illustrated.  {Subscrip- 
tion.) Cloth,  $27.50  ;  %  mor.,  $38.50 
Special  Descriptive  Circular  will  be  sent  upon  application. 

DAVIS.    Materia  Medica  and  Prescription  Writing.        $1.50 

GORGAS.  Dental  Medicine.  A  Manual  of  Materia  Medica  and 
Therapeutics.     7th  Edition,  Revised.  $4.00 

GROFF.  Materia  Medica  for  Nurses,  with  questions  for  Self  Exam- 
ination.    2d  Edition,  Revised  and  Improved.  In  Press. 

HELLER.  Essentials  of  Materia  Medica,  Pharmacy,  and 
Prescription  Writing.  $1.50 

MAYS.    Theine  in  the  Treatment  of  Neuralgia.    J6  bound,  .50 

POTTER.  Hand-Book  of  Materia  Medica,  Pharmacy,  and 
Therapeutics,  including  the  Action  of  Medicines,  Special  Therapeu- 
tics, Pharmacology,  etc.,  including  over  600  Prescriptions  and  For- 
mulae. 9th  Edition,  Revised  and  Enlarged.  With  Thumb  Index  in 
each  copy.    Just  Ready.  Cloth,  $5.00;  Sheep,  $6.00 

POTTER.  Compend  of  Materia  Medica,  Therapeutics,  and 
Prescription  Writing,  with  Special  Reference  to  the  Physiologi- 
cal Action  of  Drugs.     6th  Edition.  .80;  Interleaved,  $1.00 

MURRAY.     Rough  Notes  on  Remedies.    4th  Edition.         $135 


MEDICAL  BOOKS.  17 


SAYRE.  Organic  Materia  Medica  and  Pharmacognosy.  An 
Introduction  to  the  Study  of  the  Vegetable  Kingdom  and  the  Vege- 
table and  Animal  Drugs.  Comprising  the  Botanical  and  Physical 
Characteristics,  Source,  Constituents,  and  Pharmacopeial  Prepara- 
tions, Insects  Injurious  to  Drugs,  and  Pharmacal  Botany.  With 
sections  on  Histology  and  Microtechnique,  by  W.  C.  Stevens. 
374  Illustrations,  many  of  which  are  original.    2d  Edition. 

Cloth,  $4.50 

TAVERA.     Medicinal  Plants  of  the  Philippines.  $2.00 

WHITE  AND  WILCOX.  Materia  Medica,  Pharmacy,  Phar- 
macology, and  Therapeutics.  5th  American  Edition,  Revised  by 
Reynold  W.  Wilcox,  m.a.,  m.d.,  ll.d.,  Professor  of  Clinical 
Medicine  and  Therapeutics  at  the  New  York  Post-Graduate  Medical 
School.  Cloth,  $3.00;  Leather,  $3.50 

"  The  care  with  which  Dr.  Wilcox  has  performed  his  work  is  con- 
spicuous on  every  page,  and  it  is  evident  that  no  recent  drug  possess- 
ing any  merit  has  escaped  his  eye.  We  believe,  on  the  whole,  this  is 
the  best  book  on  Materia  Medica  and  Therapeutics  to  place  in  the 
hands  of  students,  and  the  practitioner  will  find  it  a  most  satisfactory 
work  for  daily  use." —  The  Cleveland  Medical  Gazette. 

MEDICAL    JURISPRUDENCE     AND 
TOXICOLOGY. 

REESE.  Medical  Jurisprudence  and  Toxicology.  A  Text-Book 
for  Medical  and  Legal  Practitioners  and  Students.  5th  Edition. 
Revised  by  Henry  Leffmann,  m.d.       C1o.,$3.oo;  Leather,  $3.50 

"  To  the  student  of  medical  jurisprudence  and  toxicology  it  is  in- 
valuable, as  it  is  concise,  clear,  and  thorough  in  every  respect." — The 
American  Journal  of  the  Medical  Sciences. 

MANN.    Forensic  Medicine  and  Toxicology.    Illus.  £6.50 

TANNER.  Memoranda  of  Poisons.  Their  Antidotes  and  Tests. 
8th  Edition,  by  Dr.  Henry  Leffmann.  .75 

MICROSCOPY. 

CARPENTER.  The  Microscope  and  Its  Revelations.  8th 
Edition,  Revised  and  Enlarged.      817  Illustrations  and  23   Plates. 

Cloth,  |8.oo ;  Half  Morocco,  $9.00 

LEE.  The  Microtomist's  Vade  Mecum.  A  Hand-Book  of 
Methods  of  Microscopical  Anatomy.  887  Articles.  5th  Edition, 
Enlarged.  $4.00 

OERTEL.  Medical  Microscopy.  A  Guide  to  Diagnosis,  Ele- 
mentary Laboratory  Methods  and  Microscopic  Technic.  120  Illus- 
trations. Nearly  Ready. 

REEVES.  Medical  Microscopy,  including  Chapters  on  Bacteri- 
ology, Neoplasms,  Urinary  Examination,  etc.  Numerous  Illus- 
trations, some  of  which  are  printed  in  colors.  $2 .50 

WETHER  ED.  Medical  Microscopy.  A  Guide  to  the  Use  of  the 
Microscope  in  Practical  Medicine.    100  Illustrations.  $2.00 


18  SUBJECT  CATALOGUE. 

MISCELLANEOUS. 

BERRY.     Diseases  of  Thyroid  Gland.    Illustrated.  $4.00 

BURNETT.  Foods  and  Dietaries.  A  Manual  of  Clinical  Diet- 
etics.   2d  Edition.  #1.50 

BUXTON.    Anesthetics.    Illustrated.    3d  Edition.  $1.50 

COHEN.  Organotherapy.  See  Cohen,  Physiologic  Therapeutics 
page  ib. 

DAVIS.  Dietotherapy.  Food  in  Health  and  Disease.  With 
Tables  of  Dietaries,  Relative  Value  of  Foods,  etc.  See  Cohen, 
Physiologic  Therapeutics,  page  ib. 

GOULD.  Borderland  Studies.  Miscellaneous  Addresses  and 
Essays.     i2mo.  $2.00 

GREENE.  Medical  Examination  for  Life  Insurance.  Illus- 
trated.    With  Colored  and  other  Engravings.  #4.00 

HAIG.  Causation  of  Disease  by  Uric  Acid.  The  Pathology  of 
High  Arterial  Tension,  Headache,  Epilepsy,  Gout,  Rheumatism, 
Diabetes,  Bright's  Disease,  etc.     5thEdition.  $3.00 

HAIG.  Diet  and  Food.  Considered  in  Relation  to  Strength  and 
Power  of  Endurance.    3d  Edition.  $1.00 

HENRY.    A  Practical  Treatise  on  Anemia.  Half  Cloth,  .50 

LEFFMANN.     Food  Analysis.    Illustrated.  $2.50 

NEW  SYDENHAM  SOCIETY'S  PUBLICATIONS.  Circulars 
upon  application.  Per  Annum,  $8.00 

OSGOOD.    The  Winter  and  Its  Dangers.  .40 

PACKARD.     Sea  Air  and  Sea  Bathing.  .40 

RICHARDSON.     Long  Life  and  How  to  Reach  It.   ^-  .40 

ST.  CLAIR.     Medical  Latin.  $1.00 

TISSIER.     Pneumatotherapy.    See  Cohen,  Physiologic  Therapeu- 
tics, page  ib. 
TURNBULL.    Artificial  Anesthesia.     4th  Edition.    Illus.    $2.50 

WEBER  AND  HINSDALE.  Climatology  and  Health 
Resorts.  Including  Mineral  Springs.  2  Vols.  Illus'rated  with 
Colored  Maps.     See  Cohen,  Physiologic  Therapeutics ,  page  ib. 

WILSON.    The  Summer  and  Its  Diseases.  .40 

WINTERNITZ.  Hydrotherapy,  Thermotherapy,  Photo- 
therapy, Mineral  Waters,  Baths,  etc.  Illustrated.  See  Cohen, 
Physiologic  Therapeutics ,  page  lb. 


NERVOUS  DISEASES. 

DERCUM.  Rest,  Suggestion,  Mental  Therapeutics.  See 
Cohen,  Physiologic  Therapeutics, page  lb. 

GORDINIER.  The  Gross  and  Minute  Anatomy  of  the  Cen- 
tral Nervous  System.  With  271  original  Colored  and  other 
Illustrations.  Cloth,  $6.00;  Sheep,  $7.00 

GOWERS.    Syphilis  and  the  Nervous  System.  $1.00 


MEDICAL  BOOKS.  19 


GOWERS.  Manual  of  Diseases  of  the  Nervous  System.  A 
Complete  Text-Book.  Revised,  Enlarged,  and  in  many  parts  Re- 
written. With  many  new  Illustrations.  Two  volumes. 
Vol.  I.  Diseases  of  the  Nerves  and  Spinal  Cord.  3d  Edition,  En- 
larged. Cloth,  $4.00;  Sheep,  $5.00 
Vol.  II.  Diseases  of  the  Brain  and  Cranial  Nerves ;  General  and 
Functional  Disease.    2d  Edition.              Cloth,  $4.00;  Sheep,  $5.00 

GOWERS.  Epilepsy  and  Other  Chronic  Convulsive  Diseases. 
2d  Edition.  $3.00 

HORSLEY.    The  Brain  and  Spinal  Cord.    The  Structure  and 
Functions  of.    Numerous  Illustrations.  $2.50 

ORMEROD.    Diseases  of  the  Nervous  System.    66  Wood  En- 
gravings. $1.00 

PERSHING.     Diagnosis  of  Nervous  and  Mental  Diseases. 

Illustrated.  $1.25 

PRESTON.     Hysteria  and  Certain  Allied  Conditions.    Their 

Nature  and  Treatment.    Illustrated.  $2.00 

WOOD.    Brain  Work  and  Overwork.  .40 


NURSING  (see  also  Massage). 

Special  Catalogue  of  Books  for  Nurses  sent  free  upon  application. 

CANFIELD.  Hygiene  of  the  Sick-Room.  A  Book  for  Nurses  and 
Others.  Being  a  Brief  Consideration  of  Asepsis,  Antisepsis,  Disinfec- 
tion, Bacteriology,  Immunity,  Heating  and  Ventilation,  and  Kindred 
Subjects  for  the  Use  of  Nurses  and  Other  Intelligent  Women.    $1.25 

CUFF.    Lectures  to  Nurses  on  Medicine.    Third  Edition.    $1.25 

DAVIS.  Bandaging.  Its  Principles  and  Practice.  163  Original 
Illustrations.     Just  Ready.  $1.50 

DOMVILLE.  Manual  for  Nurses  and  Others  Engaged  in  At- 
tending the  Sick.  9th  Edition.  With  Recipes  for  Sick-room  Cook- 
ery, etc.  In  Press. 

FULLERTON.    Obstetric  Nursing.    41  Ills.    5th  Ed.  $1.00 

FULLERTON.     Surgical    Nursing.    3d  Ed.    69  Ills.  $1.00 

GROFF.  Materia  Medica  for  Nurses.  With  Questions  for  Self-Ex- 
amination.    2d  Edition,  Revised  and  Improved.   Just  Ready.    $1.25 

HADLEY.  General,  Medical,  and  Surgical  Nursing.  A  very 
Complete  Manual,  Including  Sick-Room  Cookery.  Just  Ready.  $1.25 

HUMPHREY.  A  Manual  for  Nurses.  Including  General 
Anatomy  and  Physiology,  Management  of  the  Sick  Room,  etc. 
23d  Edition.    79  Illustration^.  $1.00 

STARR.  The  Hygiene  of  the  Nursery.  Including  the  General 
Regimen  and  Feeding  of  Infants  and  Children,  and  the  Domestic  Man- 
agement of  the  Ordinary  Emergencies  of  Early  Life,  Massage,  etc.  6th 
Edition.    25  Illustrations.  $1.00 

TEMPERATURE  AND  CLINICAL  CHARTS.     See  page  24. 

VOSWINKEL.  Surgical  Nursing.  Second  Edition,  Enlarged. 
1x2  Illustrations.  $1.00 


20  SUBJECT  CATALOGUE. 

OBSTETRICS. 

CAZEAUX  AND  TARNIER.  Midwifery.  With  Appendix  by 
Mundb.  The  Theory  and  Practice  of  Obstetrics,  including  the  Dis- 
eases ot  Pregnancy  and  Parturition,  Obstetrical  Operations,  etc. 
8th  Edition.  Illustrated  by  Colored  and  other  full-page  Plates,  and 
numerous  Wood  Engravings.  Cloth,  #4.50 ;  Full  Leather,  $5.50 

EDGAR.  Text-Book  of  Obstetrics.  By  J.  Clifton  Edgar, 
m.d.,  Professor  of  Obstetrics,  Medical  Department  of  Cornell 
University,  New  York  City.     Elaborately  Illustrated.  In  Press. 

FULLERTON.    Obstetric  Nursing.     5th  Ed.    Illustrated.    $1.00 

LANDIS.    Compend  of  Obstetrics.    7th  Edition,  Revised  by  Wm. 

H.  Wells,  Demonstrator  of  Clinical  Obstetrics,  Jefferson  Medical 

College.    52  Illustrations.  .80;  Interleaved,  $1.00 

WINCKEL.  Text-Book  of  Obstetrics,  Including  the  Pathol- 
ogy and  Therapeutics  of  the  Puerperal  State.    Illus.    $5.00 

PATHOLOGY— BACTERIOLOGY. 

BARLOW.    General  Pathology.    795  pages.    8vo.  $5.00 

BLACK.     Micro-Organisms.    The  Formation  of  Poisons.  .75 

BLACKBURN.    Autopsies.    A  Manual  of  Autopsies  Designed  for 

the  Use  of  Hospitals  for  the  Insane  and  other  Public  Institutions. 

Ten  full-page  Plates  and  other  Illustrations.  $1.25 

CONN.    Agricultural  Bacteriology.    Illustrated.  $2.50 

CONN.     Bacteria  in  Milk  Products.     Illustrated.  In  Press. 

COPLIN.  Manual  of  Pathology.  Including  Bacteriology,  Technic 
of  Post-Mortems,  Methods  of  Pathologic  Research,  etc.  330  Illus- 
trations, 7  Colored  Plates.     3d  Edition.  fr}-50 

DA  COSTA.  Clinical  Hematology.  A  Practical  Guide  -tcsthe 
Examination  of  the  Blood.  Six  Colored  Plates  and  48  Illustrations. 
Just  Ready.  Cloth,  $5.00 ;  Sheep,  $6.00 

EMERY.  Bacteriological  Diagnosis.  2  Colored  Plates  and  32 
other  Illustrations.    Just  Ready.  $1.50 

HEWLETT.  Manual  of  Bacteriology.  75  Illustrations.  Second 
Edition,  Revised  and  Enlarged.    Just  Ready.  $4.00 

ROBERTS.   Gynecological  Pathology.  Illustrated.  $6.00 

THAYER.       Compend    of    General    Pathology.       Illustrated. 

Just  Ready.     .80 ;  Interleaved,  $1.00 

THAYER.     Compend  of  Special  Pathology.     Illustrated. 

Just  Ready.    .80 ;  Interleaved,  $1.00 

VIRCHOW.     Post-Mortem  Examinations.    3d  Edition.         .75 

WHITACRE.  Laboratory  Text-Book  of  Pathology.  With 
121  Illustrations.  $i-5o 

WILLIAMS.  Bacteriology.  A  Manual  for  Students.  90  Illus- 
trations.    2d  Edition,  Revised.  $1.50 


PHARMACY. 

Special  Catalogue  of  Books  on  Pharmacy  sent  free  upon  application. 

COBLENTZ.  Manual  of  Pharmacy.  A  Complete  Text-Book 
by  the  Professor  in  the  New  York  College  of  Pharmacy.  2d  Edition, 
Revised  and  Enlarged.   437  Illus.  Cloth,  $3.50;  Sheep,  $4.50 

COBLENTZ.    Volumetric  Analysis.    Illustrated.  $1.25 


MEDICAL   BOOKS.  21 


BEASLEY.  Book  of  3100  Prescriptions.  Collected  from  the 
Practice  of  the  Most  Eminent  Physicians  and  Surgeons — English, 
French,  and  American.  A  Compendious  History  ot  the  Materia 
Medica,  Lists  of  the  Doses  of  all  the  Officinal  and  Established  Pre- 
parations, an  Index  of  Diseases  and  their  Remedies.     7th  Ed.     $2.00 

BEASLEY.  Druggists'  General  Receipt  Book.  Comprising 
a  Copious  Veterinary  Formulary,  Recipes  in  Patent  and  Proprietary 
Medicines,  Druggists'  Nostrums,  etc. ;  Perfumery  and  Cosmetics, 
Beverages,  Dietetic  Articles  and  Condiments,  Trade  Chemicals, 
Scientific  Processes,  and  many  Useful  Tables.     10th  Ed.  $2.00 

BEASLEY.  Pharmaceutical  Formulary.  A  Synopsis  of  the 
British,  French,  German,  and  United  States  Pharmacopoeias.  Com- 
prising Standard  and  Approved  Formulae  for  the  Preparations  and 
Compounds  Employed  in  Medicine.     12th  Edition.  $2.00 

PROCTOR.  Practical  Pharmacy.  3d  Edition,  with  Illustrations 
and  Elaborate  Tables  of  Chemical  Solubilities,  etc.  $3-°° 

ROBINSON.     Latin  Grammar  of  Pharmacy  and   Medicine. 

3d  Edition.     With  elaborate  Vocabularies.  $I-75 

SAYRE.    Organic  Materia  Medica  and  Pharmacognosy.    An 

Introduction  to  the  Study  of  the  Vegetable  Kingdom  and  the  Vege- 
table and  Animal  Drugs.  Comprising  the  Botanical  and  Physical 
Characteristics,  Source,  Constituents,  and  Pharmacopeial  Prepar- 
ations, Insects  Injurious  to  Drugs,  and  Parmacal  Botany.  With 
sections  on  Histology  and  Microtechnique,  by  W.  C.  Stevens. 
374  Illustrations.    Second  Edition.  Cloth,  $4.50 

SCOVILLE.  The  Art  of  Compounding.  Second  Edition,  Re- 
vised and  Enlarged.  Cloth,  #2.50 

STEWART.  Compend  of  Pharmacy.  Based  upon  "  Reming- 
ton's Text-Book  of  Pharmacy."  5th  Edition,  Revised  in  Accord- 
ance with  the  U.  S.  Pharmacopoeia,  1890.  Complete  Tables  ot 
Metric  and  English  Weights  and  Measures.     .80 ;   Interleaved,  $1.00 

TAVERA.     Medicinal  Plants  of  the  Philippines.  $2.00 

UNITED  STATES  PHARMACOPOEIA.  7th  Decennial  Revision. 
Cloth,  $2.50  (postpaid,  #2.77) ;  Sheep,  $3.00  (postpaid,  $3.27) ;  Inter- 
leaved, $4.00  (postpaid,  $4.50);  Printed  on  one  side  of  page  only, 
unbound,  $3.50  (postpaid,  #3.90). 

Select  Tables  from  the  U.  S.  P.    Being  Nine  of  the  Most  Impor- 
tant and  Useful  Tables,  Printed  on  Separate  Sheets.  .25 
POTTER.      Hand-Book  of  Materia  Medica,  Pharmacy,  and 
Therapeutics.    600  Prescriptions.    8th  Ed.    Clo.,  $5.00;  Sh.,  $6.00 


PHYSIOLOGY. 

BIRCH.     Practical    Physiology.     An  Elementary  Class  Book. 

62  Illustrations.  $i-75 

BRUBAKER.    Compend  ot  Physiology.    10th  Edition,  Revised 

and  Enlarged.     Illustrated.  .80;  Interleaved,  $1. 00 

JONES.    Outlines  of  Physiology.    96  Illustrations.  $*-5<> 

KIRKES.  Handbook  of  Physiology.  17th  Authorized  Edition. 
Revised,  Rearranged,  and  Enlarged.  By  Prof.  W.  D.  Hallibur- 
ton, of  Kings  College,  London.  681  Illustrations,  some  of  which 
are  in  colors.  Cloth,  $3.00;  Leather,  $3.75 


22  SUBJECT  CATALOGUE. 

LANDOIS.  A  Text-Book  of  Human  Physiology,  Including 
Histology  and  Microscopical  Anatomy,  with  Special  Reference  to 
the  Requirements  of  Practical  Medicine.  5th  American,  translated 
from  the  last  German  Edition,  with  Additions  by  Wm,  Stirling, 
m.d.,d.sc.    845  Illus.,  many  of  which  are  printed  in  colors.   In  Press. 

STARLING.     Elements  of  Human  Physiology.    100 Ills.   $1.00 

STIRLING.  Outlines  of  Practical  Physiology.  Including 
Chemical  and  Experimental  Physiology,  with  Special  Reference  to 
Practical  Medicine.     3d  Edition.     289  Illustrations.  $2.00 

TYSON.    Cell  Doctrine.    Its  History  and  Present  State.        fci.50 

PRACTICE. 

BEALE.    On  Slight  Ailments;  their  Nature  and  Treatment. 

2d  Edition,  Enlarged  and  Illustrated.  $}-*S 

FAGGE.  Practice  of  Medicine.  4th  Edition,  by  P.  H.  Pye- 
Smith,  m  d.     2  Volumes.  Vol.  I,  $6  00  ;  Vol.  II,  In  Press. 

FOWLER.  Dictionary  of  Practical  Medicine.  By  various 
writers.  An  Encyclopaedia  of  Medicine.  Clo.,$3.oo;  Half  Mor.  $4.00 
GOULD  AND  PYLE.  Cyclopedia  of  Practical  Medicine  and 
Surgery.  A  Concise  Reference  Handbook,  with  particular  Refer- 
ence to  Diagnosis  and  Treatment.  Edited  by  Drs.  Gould  and 
Pyle,  Assisted  by  72  Special  Contributors.  Illustrated,  one  volume. 
Large  Square  Octavo,  Uniform  with  "Gould's  Illustrated  Diction- 
ary." Sheep  or  Half  Mor.,  $10  00  ;  with  Thumb  Index,  $11.00 

Half  Russia,  Thumb  Index,  $12  00 
j8SP*  Complete  descriptive  circular  free  upon  application. 
GOULD  AND  PYLE'S  Pocket  Cyclopedia  of  Medicine  and 
Surgery.     Based   upon   the   above   and    Uniform   with   "  Gould's 
Pocket  Dictionary." 

Full  Limp  Leather,  Gilt  Edges,  Round  Corners,  $1.00 
With  Thumb  Index,  $1.25 
HUGHES.    Compend  of  the  Practice  of  Medicine.    6th  Edition, 
Revised  and  Enlarged. 

Part  I.     Continued,  Eruptive,  and  Periodical  Fevers,  Diseases  of  the 
Stomach,   Intestines,  Peritoneum,  Biliary   Passages,  Liver,  Kid- 
neys, etc.,  and  General  Diseases,  etc. 
Part  II.     Diseases  of  the  Respiratory  System,  Circulatory  System, 
and  Nervous  System;  Diseases  of  the  Blood,  etc. 

Price  of  each  part,  .80;  Interleaved,  $1.00 

Physician's   Edition.      In  one  volume,  including  the  above  two 

parts,  a   Section  on  Skin   Diseases,  and  an  Index.     6th  Revised 

Edition.    625  pp.  Full  Morocco,  Gilt  Edge,  $2.25 

MURRAY.     Rough  Notes  on  Remedies.    4th  Ed.  $1.25 

TAYLOR.    Practice  of  Medicine.    6th  Edition.  $4.00 

TYSON.  The  Practice  of  Medicine.  By  James  Tyson,  m.d., 
Professor  of  Medicine  in  the  University  of  Pennsylvania.  A  Com- 
plete Systematic  Text-book  with  Special  Reference  to  Diagnosis  and 
Treatment.  2d  Edition,  Enlarged  and  Revised.  Colored  Plates  and 
125  other  Illustrations.     1222  Pages.       Cloth,  $5.50  ;  Leather,  $6.50 

STOMACH.     INTESTINES. 

HEMMETER.  Diseases  of  the  Stomach.  Their  Special  Path- 
ology, Diagnosis,  and  Treatment.  With  Sections  on  Anatomy, 
Analysis  of  Stomach  Contents,  Dietetics,  Surgery  of  the  Stomach, 
etc.  3d  Edition,  Revised.  With  15  Plates  and  41  other  Illustrations, 
a  number  of  which  are  in  Colors.    Just  Ready 

Cloth,  $6.00;  Sheep,  $7.00 


MEDICAL  BOOKS.  23 


HEMMETER.  Diseases  of  the  Intestines.  Their  Special  Path- 
ology, Diagnosis,  and  Treatment.  With  Sections  on  Anatomy  and 
Physiology,  Microscopic  and  Chemic  Examination  of  Intestinal 
Contents,  Secretions,  Feces  and  Urine,  Intestinal  Bacteria  and 
Parasites,  Surgery  of  the  Intestines,  Dietetics,  Diseases  of  the 
Rectum,  etc.  With  Full-page  Colored  Plates  and  many  other 
Original  Illustrations.     2  Volumes.     Octavo.    Just  Ready. 

Price  of  each  Volume,  Cloth,  $5.00;  Sheep,  $6.00 

SKIN. 

BULKLEY.    The  Skin  in  Health  and  Disease.    Illustrated.    .40 

CROCKER.  Diseases  of  the  Skin.  Their  Description,  Pathol- 
ogy, Diagnosis,  and  Treatment,  with  Special  Reference  to  the  Skin 
Eruptions  of  Children.  3d  Edition,  Thoroughly  Revised.  With 
New  Illustrations.  Nearly  Ready.    $5.00 

SCHAMBERG.  Diseases  of  the  Skin.  2d  Edition,  Revised  and 
Enlarged.    105  Illustrations.    Being  No.  16  ?  Quiz-Compend  ?  Series. 

Cloth,  .80;  Interleaved,  $1.00 

VAN  HARLINGEN.  On  Skin  Diseases.  A  Practical  Manual 
of  Diagnosis  and  Treatment,  with  special  reference  to  Differential 
Diagnosis.  3d  Edition,  Revised  and  Enlarged.  With  Formulae 
and  60  Illustrations,  some  of  which  are  printed  in  colors.        $2.75 

SURGERY  AND  SURGICAL  DIS- 
EASES (see  also  Urinary  Organs). 

BERRY.  Diseases  of  the  Thyroid  Gland  and  Their  Surgical 
Treatment.     Illustrated.  $4.00 

BUTLIN.  Operative  Surgery  of  Malignant  Disease.  2d  Edi- 
tion.    Illustrated.     Octavo.  $4-5Q 

DAVIS.  Bandaging.  Its  Principles  and  Practice.  163  Original 
Illustrations.  $1.50 

DEAVER.  Surgical  Anatomy.  A  Treatise  on  Human  Anatomy 
in  its  Application  to  Medicine  and  Surgery.  With  about  450  very 
Handsome  full-page  Illustrations  Engraved  from  Original  Drawings 
made  by  special  Artists  from  Dissections  prepared  for  the  purpose. 
Three  Volumes.  Royal  Square  Octavo. 
Cloth,  $21.00;  Half  Morocco  or  Sheep,  $24.00  ;  Half  Russia,  $27.00 

Complete  descriptive  circular  and  special  terms  upon  application. 

DEAVER.  Appendicitis,  Its  Symptoms,  Diagnosis,  Pathol- 
ogy. Treatment,  and  Complications.  Elaborately  Illustrated 
with  Colored  Plates  and  other  Illustrations.    3d  Edition.   Preparing. 

DULLES.    What  to   Do   First  in  Accidents  and   Poisoning. 

5th  Edition.     New  Illustrations.  $1.00 

FULLERTON.     Surgical  Nursing.    3d  Edition.    69  Illus.    $1.00 

HAMILTON.    Lectures  on  Tumors.    3d  Edition.  $1.25 

HEATH.  Minor  Surgery  and  Bandaging.  12th  Edition,  Revised 
and  Enlarged.     195  Illus.,  Formulae,  Diet  List,  etc.  $150 

HEATH.  Clinical  Lectures  on  Surgical  Subjects.  Second 
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very  much  Enlarged  and  Rearranged.   167  Illustrations,  c-8  Formulae. 

Cloth,  .80;  Interleaved,  $1.00 


24  SUBJECT  CATALOGUE. 

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KEAY.     Medical  Treatment  of  Gall  Stones.    Just  Ready.  $1.25 

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Illustrated.  $4.00 

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Treatment.  3d  American  Edition.  Revised  and  edited  by  John  B. 
Hamilton,  m.d.,  ll.d.,  Professor  of  the  Principles  of  Surgery  and 
Clinical  Surgery,  Rush  Medical  College,  Chicago.  623  Illustrations, 
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SMITH.  Abdominal  Surgery.  Being  a  Systematic  Description  of 
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VOSWINKEL.  Surgical  Nursing.  Second  Edition,  Revised  and 
Enlarged.     11 1  Illustrations.  $1.00 

WALSHAM.  Manual  of  Practical  Surgery.  7th  Ed.,  Re- 
vised and  Enlarged.  483  Engravings.  950  pages.  #3-5° 


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Diseases.     7th  Revised  and  Enlarged  Ed.     12010.  $1-25 


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BYFORD    (H.  T.).     Manual   of   Gynecology.     Third    Edition, 
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DUHRSSEN.     A  Manual    of  Gynecological    Practice.     105 
Illustrations.  $1.50 

FULLERTON.     Surgical  Nursing.     3d  Edition,  Revised  and 
Enlarged.    69  Illustrations.  $1.00 

LEWERS.     Diseases  of  Women.    146  Illus.    5th  Ed.  $2.50 

MONTGOMERY.     Practical    Gynecology.     A  Complete  Sys- 
tematic Text-Book.    527  Illustrations.     Cloth,  $5.00;  Leather,  $6.00 

ROBERTS.      Gynecological    Pathology.     With  127  Full-page 
Plates  containing  151  Figures.  $6.00 

WELLS.    Compend  of  Gynecology.    Illustrated.    2d  Edition. 

.80;  Interleaved,  %  1 .00 


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could  be  found  for  either  student  or  practitioner." — Southern  Clinic. 


BLAKISTON'S  ?  QUIZ-COMPENDS? 

The  Best  Series  of  Manuals  for  the  Use  of  Students. 
Price  of  each,  Cloth,  .80.         Interleaved,  for  taking  Notes,  $1.00. 

These  Compends  are  based  on  the  most  popular  text-books  and 
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vised, so  that  they  may  thoroughlv  represent  the  present  state  of  the 
subjects  upon  which  they  treat.  The  authors  have  had  large  experi- 
ence as  Quiz-Masters  and  attaches  of  colleges,  and  are  well  acquainted 
with  the  wants  of  students.  They  are  arranged  in  the  most  ap- 
proved form,  thorough  and  concise,  containing  nearly  iooo  illustra- 
tions and  lithograph  plates,  inserted  wherever  they  could  be  used  to 
advantage.  Can  be  used  by  students  of  any  college.  They  contain 
information  nowhere  else  collected  in  such  a  condensed, practical  shape. 

No.  i.  POTTER.     HUMAN   ANATOMY.    Sixth  Edition.     117 

Illustrations  and  16  Plates  of  Nerves  and  Arteries. 
No.  2.  HUGHES.   PRACTICE  OF  MEDICINE.  Part  I.  Sixth 

Edition,  Enlarged  and  Improved. 

No.  3.  HUGHES.      PRACTICE    OF    MEDICINE.      Part   II. 

Sixth  Edition,  Revised  and  Improved. 

No.  4.    BRUBAKER.     PHYSIOLOGY.     Tenth  Edition.    Illus. 

No.  5.  LANDIS.     OBSTETRICS.     Seventh  Edition.      52  Illus. 

No.  6.  POTTER.     MATERIA    MEDICA,    THERAPEUTICS, 

AND  PRESCRIPTION  WRITING.    Sixth  Revised  EditioD. 

No.  7.   WELLS.     GYNECOLOGY.     Second  Ed.     14c1  IUus. 
No.  8.    GOULD   AND   PYLE.      DISEASES  OF    THE  EYE. 

Second  Edition.    Refraction,  Treatment,  Surgery,  etc.    109  Illus. 

No.   9.    HORWITZ.      SURGERY.       Including    Minor    Surgery, 
Bandaging,  Surgical  Diseases,  Differential  Diagnosis  and  Treat-* 
ment.    Fifth  Edition.    With  98  Formulae  and  71  Illustrations. 

No.  10.  LEFFMANN.     MEDICAL    CHEMISTRY.      Fourth 

Edition.     Including  Urinalysis,  Animal  Chemistry,  Chemistry  of 
Milk,  Blood,  Tissues,  the  Secretions,  etc. 

No.  11.  STEWART.  PHARMACY.  Fifth  Edition.  Based  upon 
Prof.  Remington's  Text-Book  of  Pharmacy. 

No.  12.  BALLOU.  VETERINARY  ANATOMY  AND  PHY- 
SIOLOGY.    29  graphic  Illustrations. 

No.  13.  WARREN.  DENTAL  PATHOLOGY  AND  DEN- 
TAL MEDICINE.     Third  Edition,  Illustrated. 

No.  14.  HATFIELD.      DISEASES  OF  CHILDREN.    3d  Ed. 

No.  15.  THAYER.     GENERAL  PATHOLOGY.     78  Illus. 

No.  16.  SCHAMBERG.     DISEASES  OF  THE  SKIN.   Second 

Edition,  Revised  and  Enlarged.     105  Illustrations. 

No.  17.  CUSHING.     HISTOLOGY.     Illustrated. 
No.  18.  THAYER.     SPECIAL  PATHOLOGY.    34  Illustrations. 
Careful  attention  has  been  given  to  the  construction  of  each  sentence, 
and  while  the  books  will  be  found  to  contain  an  immense  amount  of 
knowledge  in  small  space,  they  will  likewise  be  found  easy  reading. 

26 


^ 


DA   COSTA 


Clinical   Hematology 


A  Practical  Guide  to  the  Examination  of  the  Blood  by 
Clinical  Methods.  With  Reference  to  the  Diagnosis  of 
Disease.     With  Colored  Illustrations.  Cloth,  $5.00 

*^*  A  new,  thorough,  systematic,  and  comprehensive 
work,  its  purpose  being,  first,  to  show  how  to  examine  the 
blood,  and  second,  how  to  diagnose  from  such  examination 
diseases  of  the  blood  itself  and  general  diseases.  The 
author's  aim  has  been  to  cover  not  alone  the  field  of  original 
research,  but  to  supply  a  book  for  the  student,  the  hospital 
physician  and  the  general  practitioner.  It  will  be  found 
wanting  in  none  of  these  respects. 

OERTEL 


Medical  Microscopy 

NEARLY  READY 

A  GUIDE  TO  DIAGNOSIS,  ELEMEN- 
TARY LABORATORY  METHODS, 
AND     MICROSCOPIC    TECHNIC 

By  T.   E.   Oertel,  M.D., 

Professor  of  Pathology  and  Clinical  Microscopy,  Medical  Depart- 
ment, University  of  Georgia. 

WITH   120  ILLUSTRATIONS 

27 


JACOBSON'S 
Operations  of  Surgery 


The  Operations  of  Surgery.  By  W.  H.  A. 
Jacobson,  f.r.c.s.,  Surgeon  to  Guy's  Hospital; 
Consulting  Surgeon  Royal  Hospital  for  Children 
and  Women;  Member  Court  of  Examiners  Royal 
College  of  Surgeons;  Joint  Editor  Annals  of  Sur- 
gery; and  F.  J.  Steward,  f.r.c.s.,  Assistant 
Surgeon  Guy's  Hospital  and  to  the  Hospital  for 
Sick  Children.  Fourth  Edition,  Revised,  En- 
larged and  Improved.  550  Illustrations.  Two 
Volumes,   Octavo,    1524  pages.        Cloth),  $10.00 

Sheep,  $12.00 

PRESS  NOTICES  OF  FORMER  EDITIONS 

"  The  author  proves  himself  a  judicious  operator,  as 
shown  by  his  choice  of  methods  and  by  the  emphasis  with 
which  he  refers  to  the  different  dangers  and  complications 
which  may  arise  to  mar  success  or  jeopardize  life." — New 
York  Medical  Record. 

"  The  important  anatomical  points  are  clearly  set  forth, 
the  conditions  indicating  or  contraindicating  operative  inter- 
ference are  given,  the  details  of  the  operations  themselves 
are  brought  forward  prominently,  and  frequently  the  after- 
treatment  is  considered.  Herein  is  one  of  the  strong  points 
of  the  book." — New  York  Medical  Journal. 

28 


The  Pocket  Cyclopedia,  of 
Medicine   and   Surgery 

Full  Limp  Leather,  Round  Corners,  Gilt  Edges,  $1.00 
With  Thumb  Index,  $1.25 

Uniform  'with  "Gould's  Pocket  Dictionary" 


A  concise  practical  volume  of  nearly  600 
pages,  containing  a  vast  amount  of  infor- 
mation on  all  medical  subjects,  including 
Diagnosis  and  Treatment  of  Disease, 
with  Formulas  and  Prescriptions,  Emer- 
gencies, Poisons,  Drugs  and  Their  Uses, 
Nursing,  Surgical  Procedures,  Dose  List 
in  both  English  and  Metric  Systems,  etc. 

By  Drs.  Gould  and  Pyle 

Based  upon  their  large  u  Cyclopedia  of 
Medicine  and  Surgery/*      J*       <£       jt 


*.£*  This  is  a  new  book  which  will  prove  of  the  greatest 
value  to  students.  It  is  to  the  broad  field  of  general  medi- 
cal information  what  "Gould's  Pocket  Dictionary"  is  to 
the  more  special  one  of  definition  and  pronunciation  of 
words.  The  articles  are  concise  but  thorough,  and  arranged 
in  shape  for  quick  reference.  In  no  other  book  can  be 
found  so  much  exact  detailed  knowledge  so  conveniently 
classified,  so  evenly  distributed,  so  methodically  grouped. 
It  is  Multum  in  Parvo. 

29 


A  NEW  EDITION 


Crocker  on  the  Skin 


The  Diseases  of  the  Skin.  Their  Description,  Pathology, 
Diagnosis,  and  Treatment,  with  Special  Reference  to  the 
Skin  Eruptions  of  Children.  By  H.  Radcliffe  Crocker, 
m.d.  ,  Physician  to  the  Department  of  Skin  Diseases,  Uni- 
versity College  Hospital,  London.     With  new  Illustrations. 

Third  Edition,  Rewritten  and  Enlarged 

NEARLY  READY  j  CLOTH,  $5.00 

*#*  This  new  edition  will  easily  hold  the  high  position 
given  the  previous  printings.  The  author  is  a  member  of 
American,  English,  French,  German,  and  Italian  Dermalo- 
logical  Societies,  and  a  recognized  authority  the  world  over. 


STURGIS— MANUAL  OF 
VENEREAL  DISEASES 


By  F.  R.  Sturgis,  m.d.,  Sometime  Clinical  Professor  of 
Venereal  Diseases  in  the  Medical  Department  of  the  Uni- 
versity of  the  City  of  New  York.  Seventh  Edition,  Revised 
and  in  Part  Rewritten  by  the  Author  and  FoLLEN  Cabot, 
M.D.,  Instructor  in  Genito-Urinary  and  Venereal  Diseases 
in  the  Cornell  University  Medical  College.  i2mo.  216 
pages.  Cloth,  $1.25 

*x*  This  manual  was  originally  written  for  students' 
use,  and  is  as  concise  and  as  practical  as  possible.  It  pre- 
sents a  careful,  condensed  description  of  the  commoner 
forms  of  venereal  diseases  which  occur  in  the  practice  of 
the  general  physician,  together  with  the  most  approved 
remedies. 

30 


FOR  THE  DISSECTING  ROOM 

Holden's  Anatomy — Seventh  Edition 
320  Illustrations 

A  Manual  of  the  Dissections  of  the  Human  Body.  By  John 
LANGTON,  f.r.c.s.  Carefully  Revised  by  A.  HKWSON,  m.D., 
Demonstrator  of  Anatomy.  Jefferson  Medical  College,  Phila- 
delphia, etc.  320  Illustrations.  Two  small  compact  vol- 
umes.     i2mo. 

Vol.  I.  Scalp,  Face,  Orbit,  Neck,  Throat,  Thorax,  Upper 
Extremity.     435  pages.      153  Illustrations. 

Oil  Cloth,  $1.50 

Vol.  II.  Abdomen,  Perineum,  Lower  Extremity,  Brain, 
Eye,  Ear,  Mammary  Gland,  Scrotum,  Testes. 
445  pages.      167  Illustrations. 

Oil  Cloth,  $1.50 

Each   volume  sold  separately. 


Hughes    a.nd    Keith  —  Dissections 
Illustrated 

A  Manual  of  Dissections  by  Alfred  W.  Hughes,  m.b., 
m.R.C.s.  (Edin. ),  late  Professor  of  Anatomy  and  Dean  of 
Medical  Faculty,  King's  College,  London,  etc. ,  and  Arthur 
Keith,  M.D.,  Joint  Lecturer  on  Anatomy,  London  Hospital 
Medical  College,  etc.  In  three  parts.  With  527  Colored 
and  other  Illustrations. 

I.     Upper  and  Lower  Extremity.     38  Plates,  116  other 
Illustrations.  Cloth,  $3.00 

II.      Abdomen.     Thorax.     4    Plates,    149    other   Illus- 
trations. Cloth,  $3.00 
III.      Head,   Neck,  and  Central  Nervous   System.       16 
Plates,  204  other  Illustrations.           Cloth,  S3. 00 

Each  volume  sold  separately. 

*.£*  The  student  will  find  it  of  great  advantage  to  have 
a  "Dissector"  to  supplement  his  regular  text-book  on 
anatomy.  These  books  meet  all  requirements,  and  as  they 
can  be  purchased  in  parts  as  wanted,  the  outlay  is  small. 

31 


EDGAR'S 

OBSTETRICS 

A   NEW   TEXT -BOOK 


The  Illustrations  in  Edgar's  Ob- 
stetrics surpass  in  number,  in  artistic 
beauty,  and  in  practical  worth  those 
in  any  book  of  similar  character.  They 
are  largely  from  original  sources,  are 
made  to  a  scale,  and  have  been  drawn 
by  artists  of  long  experience  in  this 
class  of  medical  work. 
The  Text  has  been  prepared  with 
great  care.  The  author's  extensive  ex- 
perience in  hospital  and  private  prac- 
tice and  as  a  teacher,  his  cosmopolitan 
knowledge  of  literature  and  methods, 
and  an  excellent  judgment  based  upon 
these  particularly  fit  him  to  prepare 
what  must  be  a  standard  work. 

/  N     P  R  E  s  s 


JUST  READY 

c/L    Companion    Volume    to    Gould's     Tocket    dictionary 

A  POCKET  CYCLOPEDIA 

OF 

MEDICINE  *  SVRGERY 

EDITED  BY 

GEORGE  M.  GOVLD,  A.M.,  M.D. 

Author  of  **  Gould's  Medical  Dictionaries  %  **  Editor  of  **  American  Medicine  " 

AND 

WALTER  L.  PYLE,  A.M.,  M.D. 

Assistant  Surgeon  Wills  Eye  Hospital,  Philadelphia  j  formerly  Editor 
"International  Medical  Magazine,"  etc. 


BEING  BASED  UPON  GOULD  AND  PYLE'S  LARGE  "  CYCLOPEDIA  OF 
PRACTICAL  MEDICINE  AND  SURGERY" 


Vniform  with  Gould's  Pocket  Dictionary.    64mo.    Flexible  Leather, 
Gilt  Edges,  Round  Comers,  net  $1.00;  with  Thumb  Index.  $1.25 


T*  HIS  book  bears  to  Gould  and  Pyle's  large  "  Cyclopedia  of  Medicine 
and  Surgery ' '  a  relation  similar  to  that  which  the  Pocket  Dic- 
tionary bears  to  Gould's  complete  "Illustrated  Dictionary."  As 
the  Dictionary  gives  the  derivation,  pronunciation,  and  definition 
of  medical  words,  the  Cyclopedia  is  designed  to  furnish  general 
information  concerning  medical  subjects.  Every  subject,  concerning  which 
the  student  may  desire  a  brief  and  thorough  description,  supplementing  the 
mention  which  may  be  given  in  lectures  or  a  general  text-book,  is  taken  up 
and  treated  thoroughly  and  concisely.  To  those  desiring  concise  authoritative 
information  on  medical  or  surgical  themes  or  who  wish  to  look  up  any  new 
term  or  matter  of  recent  discovery  and  use,  the  book  will  prove  invaluable. 
It  includes  articles  on  Emergencies,  Hygiene,  Poisons,  Nursing,  etc.;  describes 
Drugs  and  their  Uses  ;  gives  Treatment  of  Diseases  ;  explains  Surgical  Oper- 
ations ;  contains  many  Prescriptions  and  Formulae,  Tables  of  Differential 
Diagnosis,  Dose  Table  in  both  English  and  Metric  Systems,  etc. 


P.  BLAKISTON'S  SON   ©.   CO.,  Publishers  and  Booksellers 
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-drfulimtp  Medical  . 

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